I am running 12.04-64bit on a Dell xps15z and the resolution changes after each reboot to 1024x768 .As a result my desktop occupies just 3/4 of my entire screen...I have to manually adjust it through the display option to the max 1366x768 in order for the desktop to occupy the whole display!If you add this to the "system problem detected" that pops up every day I cannot hide my dissatisfaction and frustration about 12.04...
Ok, try this:
After You log in set required resolution and open Your terminal and write:
Your graphical environment will be closed. After that press
and log in the text mode. Then create Xorg file:
after that write:
Did that help??