More detail is needed,... like hardware specs, which DE is being used (gnome, kde, etc.), what you are doing when you log out, etc.
But to clarify, you ARE getting your graphical login at boot, right?!?!
PS: Apparently, you are not alone with this issue,... I believe it may relate to newer Inter video chipsets, but cannot say for sure.
If you don't mind experimenting, try installing KDE, and switch to the kdm login manager (you should be able to select a gnome session from kdm logins). Let us know whether this affects the kdm login manager, or just gdm...
Last edited by JaseP; 10-03-2012 at 02:47 PM.