I've got an 8800 GTX GPU and I have enabled the restricted drivers in Ubuntu. The problem with that is that when I login (submit my password) the system hangs. I can see the desktop background, can move the mouse and that's it. Ctrl+Alt+Del won't even work, have to use Ctrl+Alt+SysRq+B to reboot.

However, I have found a workaround to this. If I restart X (Ctrl+Alt+Backspace) while on the login screen and login right after, everything works fine, I get dekstop effects, etc.

Could someone please explain why the system hangs upon login but works fine if X is restarted before that? Any solutions you could recommend?