Q:

Motivation to write the dreaded dissertation

Ok... so I have hated graduate school since day one but have slogged through because I couldn't find anything else to do (I have applied for hundreds of jobs as an escape route with no success). It has been an enormous amount of ungratifying work, especially because I am not interested in the subject I am studying and am not interested in the obtuse contributions of the study. But I am only a dissertation away from completing my PhD and being finished with my poor decision, but I am having enormous difficulty finding motivation to write it. I sit down every day and nothing comes out. I can't find the energy to read any more boring articles I need to cite or find the energy to write a complete sentence. Every time I start I find an excuse to distract myself and I don't know how to find external motivation since I lack internal motivation.
Exacerbating my lack of motivation is that I am skeptical that this degree will lead to employment (if I would want it in this field of study anyway): as I haven't been interested in my subject I haven't made the connections and done all of the networking I think is necessary to get a job with this degree, so I feel it is pretty useless to finish because I will likely have to reinvent myself after I am finished anyway. But leaving without a degree seems wrong somehow, given all this wasted effort (aren't we all subject to the sunk cost fallacy?). Any ideas on how to find the final burst of energy to finally finish?
I should add, I have already written 3 chapters and am about half through the fourth. I only need to finish the fourth, revise the 3 earlier and then write an intro and a conclusion. Plus I will need to find the energy to defend something I don't care about to my committee and the public before I can call it over. But even after all of this work it seems impossible to find the energy to write another sentence.
Update:
I wanted to thank those who chimed in and offered me kind and sincere advice. Thank you for taking time to help me, a stranger, with my life's problems. I think your suggestions were solid, practical and generally useful. I have been thinking about your advice for the month since I first posted this, and I unfortunately have to admit these strategies haven't helped me find any motivation to make much progress on my dissertation.
I thought I would respond to a few of your suggestions and see if anyone has additional thoughts or considerations.
There was the suggestion that I should go visit a counselor and to be screened for depression. I had been seeing a counselor using the services provided by the school. It is a very nice service and I have had access to what I felt was a high quality counselor, they screened me for depression and gave me the all clear. I am not depressed, although disappointed at my decisions (or lack thereof). 
I like the suggestion to talk about my work with an interested person but do not think that my work is interesting in anyway, and have no pretense that the work is contributing to make the world a better place. I don't feel the need for the work to make a difference is required to get it done and think trying to convince someone it is interesting is wasting my time and theirs. 
I think Paul Garrett hit a nerve with his comment that is at the root of my conundrum. I know continuing with something that I don't care about is a waste of my time, but the social (personal) obligation looms large and quitting this close to the finish line seems so foolish (and ire provoking for my program and committee). But despite these social pressures finding motivation to complete the daily tasks has eluded me. I know I need to finish, but the only motivation I have is to Be Finished and that isn't helping me with the daily drudgery. 
To Wolfgangs comment: part of me fully agrees with you (that I should finish because of the unknown channels that may open if I complete the phd) but part of me feels the same logic applies if I quit. I will never know the future and perhaps not completing will open up doors that wouldn't exist had I completed... and anyway because of the lack of success in getting job interviews my career counselor has suggested that I leave the phd off my resume for the jobs that are outside of academia (which are the bulk of the positions I have been applying for and don't require the phd as a qualification). This is again another factor that has sapped at my motivation to complete the degree. And this brings up a side question of how I am supposed to spin the 4 years as a phd student on my resume without saying I was a phd student (but I will ask that as a separate question at a later date). 
Given my current degree is so poorly valued by the market (or maybe it is myself) I have set a deadline of 400 job applications and if I haven't gotten an offer by that time I am going to reinvent myself (such as a job in customer service, which will have the benefit of paying more than my graduate stipend). I am at 290 now, and I only got one interview. It went well but they cancelled the position (the grant fell through). 
My tails of the job market is winding away from the original question of this post and I need to return to that. And I need to comment on the solid advice from Peter. I think is is exceptional advice and I should implement all of these practices into my life, but unfortunately I don't feel this advice pertains to this situation as doesn't help me with the core underlying issue: that I lack any interest in my work and do not have any internal motivation that comes from  connection and passion about the research I am doing. All of these practices, in my estimation, would help one to train and develop ones internal motivation, but I have little internal motivation (only guilt) for completing my work, and think it is late in the game to try and find personal connection and interest in the work and think that external pressure should be good enough (although it hasn't been enough). 
I am very happy for the people in this world who have developed a personal connection to their work and to their jobs, but I don't think that everyone is so lucky as to be personally connected to their work. I think it would be wonderful if it were the case but Peter's reason #3 is an example of the disconnect between ideal and reality. Many people in this unequal world would be ecstatic to be earning $10K a year for the chance to write papers and do research for a professor, but no amount of counting my blessings (and I am very thankful I was born into a world that allowed for the luxury of higher education) gives me the belief that the dissertation is anything but wasted time and paper. I may have felt that way in a different project, program, school, country, etc. But that isn't my luck to care about my work. And now I am not looking to find internal motivation to channel my passions to create my life's master work but to finish writing something that is good enough to pass the defense and can be forgotten about on the back-shelves of the library. I haven't been interested in what I have studied since day one and now is beyond the time to expect it to get interesting now. Of course I regret I chose this field of study and my decision to continue but I am too deep now not finish. 
Again, I don't want anyone to think I didn't appreciate their advice. I do, and think it applies to other parts of my life that I am proud of and want to develop. I am very thankful you took your valuable time to console a stranger. So I am elaborating my post today hoping I can distill the question a bit more and tap the expertise of this community, because the comments on the earlier iteration of this question were earnest and insightful. So now I ask for more help because what I think I need is a strategy to help me do something I do not want to do and hopefully there are strategies that do not require convincing myself I want to do it. So, my question for all the thinkers and experienced sages of the forum: how do you convince yourself to do something that is enormous amount of work that you don't like to do, you don't want to do, and don't think will help you but to do it anyway?

A:

Ok, so here are some things that worked for me.

Attempting to strongly connect what you are doing to avoiding negative outcomes and achieving positive outcomes. Here are some examples. If you have ever experienced unemployment (and the resultant sense of worthlessness) then make sure that you make the connection between not finishing the PhD and being unemployed clear in your mind. Similarly, if you can see ways in which the PhD will enable you to achieve goals in life then fixate on how happy those goals will make you. For me, it helped that I could connect the boring irrelevant stuff I did to the social impacts I wanted to make - I watched documentaries to help me to keep these things at the forefront of my mind.
Use cognitive behavioral therapy. This involves identifying ineffective/sub-optimal thought processes and cutting them out. For example, when I was about to start academic work, I would often spend a lot of time thinking about how pointless it was. I would think "what is the point of this" or "why do it this way when that way is so much more effective". This didn't get me anywhere - I often didn't even start the work or stopped very quickly. later, I started to cut out that thought process. Funnily, enough my technique was to imagine that I was a medieval peasant and that I had no option other than to do the work assigned. Eventually, I overcame my counterproductive habit and managed to start working whenever I needed to rather than putting things off until the last moment. 
Stop making upward comparisons with ideal situations. As related to the above I used to always compare what I was doing to what I could be doing in some perfect world where it would be the most relevant essay, or research, or whatever. That was really not a good idea as it was not a productive comparison to make. Instead it is much better to remind yourself of how lucky you are to have the opportunities you have when so much of the world does not. Sadly their are geniuses who killed themselves for want of making greater contributions when people with equal intelligence but more unfortunate circumstances were denied any chance to achieve anything at all due to no fault of their own.
Develop and maintain a positive association with your work (where possible). Basically this involves making your work something you like rather than hate (to the extent that this is possible). When I was younger I saw work as something that took me away from what made me happy. I wanted to party, play computer games, socialise etc., and work was the reason I couldn't. As a result I worked badly and did badly in academics. In turn this ensured that I got bad marks and felt bad about myself. Now things are quite different for me. I changed my perspective so that I treat my work as my personal interest - a form of personal expression and journey of learning that I treat as a priority. Partially due to this and other changes I start all tasks early and work hard on them. Inevitably I stress less than I used to and do better, which gives me more positive reinforcement. Additionally, you should try things like avoiding work when you are stressed (don't want to associate work with stress), working in places where you are calm and relaxed (I tried moving out of my office near the end of my PhD and it was a tremendous help to work in other places). Having a comfortable seat, and a quiet room at the right temperature are also very important. 
Do lots of exercise. This is crucial - most people have too much energy to spend a lot of time sitting in front of computers. I work out every day (even if it is just a short workout) so that I get to burn off excess energy. Speaking from my experience, I think that a lot of my problems in the past were due to having too much energy to relax and focus on what I was doing. Additionally exercise makes me happier and more relaxed which really helped throughout my PhD where I was occasionally too unhappy and stressed to work well.
Meet your bodies needs. A happy person works better than a stressed person in the long term. If you are not getting what you need then you will struggle to focus on other things (like work). Maybe you need to talk more with people? Maybe your brain needs novel information or situations, time in nature or whatever. You need to figure this out. For me, I need all of these things and if I don't get enough of them then I won't be working well until I do.
Have a prioritised to-do list that breaks down the tasks you need to do. I used an Eisenhower grid on evernote. One advantage of a to-do list is that it will give you a sense of productivity and success when you get things done. It is much easier to find the motivation to do something small as part of a larger goal, than to feel like you achieve nothing at the end of a day. A second advantage is that a to-do list will free you from having to remember things and keep you on track. If you can wake up and see a list of things you need to do today then you don't need to think through the "what should I do today process" - you get straight to work. A third advantage of the to-do list is that it can give you direction and clarity. Often people don't know which task to do first therefore they switch between them. However with a good to-do list and discipline you have a clear list of things to do, and an order to do them in.
If the going is really tough, and you need to get something that you hate done, then manipulate your hormones to make it easier . Your motivation and energy to act, is based on your levels of dopamine {1}. Accordingly, if, for whatever reason, these levels are extremely low, then you likely won't be act. Based on your recent update it seems that you may very well have reached a point where your levels of dopamine are too low to enable you to work. Consequently, you should consider doing things to increase them. Here are a few things that should work. First, you can take substances to increase dopamine, such as St. Johns wort,  rhodilia rosea, and nicotine (gum works with few health risks). Second, you can do more exercise {2}. Third, you can listen to music while you work {3}. All of these were useful for me at the very end of my PhD where I was very depressed at times.

That is all for now - I will add more if I think of it :). Happy also to dig up references where they might reasonably be needed.
References:
{1} Hoebel, B. G., Rada, P. V., Mark, G. P. and Pothos, E. N. (1999) 'Neural systems for reinforcement and inhibition of behavior: Relevance to eating, addiction, and depression'.
{2} Young, S. N. (2007). "How to increase serotonin in the human brain without drugs." Journal of Psychiatry & Neuroscience : JPN 32(6): 394-399.
{3} Salimpoor, V. N., Benovoy, M., Larcher, K., Dagher, A. and Zatorre, R. J. (2011) 'Anatomically distinct dopamine release during anticipation and experience of peak emotion to music', Nat Neurosci, 14(2), 257-262.

A:

Peter Slattery already answers the immediate question of how to motivate yourself. I'd just like to add one more thought about why finishing up your degree is worth it.
If you look around you and start asking how many people in their 40s or 50s are still doing the work their college degree qualified them for, you'll realize that the fraction is not actually all that large. Having a degree in one field does not lock you into employment in this field for life. What it does is open doors: you will be considered for some jobs and career steps simply because you have a degree at the required level, oftentimes regardless of the field where that degree was earned. For example, in many "traditional" companies, non-PhDs will rarely become heads of units that have a significant fraction of PhDs. You can often see this in job ads that say "expected qualification: MSc in a relevant field" or similar, where "relevant" is often broadly interpreted as long as your qualifications (not your degree) matters to those seeking to hire you.
Maybe seeing that your PhD will allow you to do things in life you wouldn't be able to do if you didn't finish it, provides you with the impulse to actually go finish it, regardless of the level of (dis)engagement you feel with the subject.

