I am using Ubuntu 11.10 with Gnome shell in my Inspiron e1505 laptop.

Specs:
Intel Core 2 Duo Processor T7200
2GB RAM
ATI X1400 graphics card

My problem is frequently, the screen freezes completely. Only the mouse pointer can be moved, no click or other interactions. Restarting gnome-shell or display manager does not fix the problem. I have to reboot system to clear the problem.

I tried gdm instead of lightdm and the problem is the same.

To try my luck, I installed 12.04 alpha and the problem is still there.

Although, when I used Fedora in the same laptop, I didn't have the problem.(but I prefer to stick to Ubuntu)

Please any suggestions or solutions.