Q:

Can't open applications menu

The applications menu in the top left corner of the screen will not open: if clicked nothing happens, the hotkey also does not work.
I am on elementary OS 0.3.1 Freya (64-bit) Quad-Core Intel® Core™ i7-4500U.

A:

I've encountered this problem before: it's caused by slingshot crashing while backgrounded. There is a very easy way to fix it.
Open a terminal, either from plank or by using the shortcut [super] + [T] and enter: 
pkill slingshot
The next time you click the applications indicator slingshot will restart and work as normal.

