Q:

Windows 7 running Virtualbox 4.1.12 with Ubuntu 10.04 LTS guest but no full screen

After a recent windows update (though may not be the issue), I am unable to run Ubuntu in the virtualbox with full screen mode.  I can no longer stretch the window to any resolution.  It is locked at 1024x768 in the guest window (Ubuntu).  For sanity, I re-installed The Linux Guest Additions.  I also tried uninstalling it and reinstalling it even though the script does this for you.  No matter what, I can't get past the limited 1024x768 workspace.  Furthermore, I noticed that xorg.conf is not in the /etc/X11 folder but I believe this is normal as my other PC running a similar setup also does not have xorg.conf yet scales the guest window of Ubuntu properly to any resolution (including true full screen mode).
I have set the guest settings to 64MB video space and also tried 128MB.  No difference there.  I also tested running Virtualbox 4.1.8 (to try an older working version).  Nothing.  Now I am back to Vbox version 4.1.12 with no avail.
I am also unable to run the Ubuntu Desktop with advanced effects.  Maybe the Linux Guest Additions is not running even though it is installed?  How do I verify this?
Any other suggestions?

A:

try with this:
1. Open terminal and enter the following command: 

sudo apt-get update
sudo apt-get install build-essential linux-headers-$(uname -r)
sudo apt-get install virtualbox-ose-guest-x11 

2. Once installation is finished, restart your virtualBox machine. 

3. Go to System -->Preferences -->Monitors and change the resolution of your screen.

source:
http://tutorial.downloadatoz.com/how-to-fix-ubuntu-10-10-virtualbox-guest-additions-problems.html

