"I was using Ubuntu 7.10 and upgraded to 8.04. After reboot, I typed login
and password and after 5 or 10 seconds nothing worked except mouse (screen
was completely frozen). I reboot (with power button) and freezes again...

I downloaded installation cd and tried to re-install it, but installation
freezes too... After 2 or 3 tries I started installation with noacpi option
and installation was succefully completed. But after login freezes again!!.

I reinstalled it with alternate cd, but nothing changes

Windows XP and Ubuntu 7.10 worked fine, but 8.04 doesn't.

I tried installing ATI propietary drivers but I had no luck Freezes again,
and again, and again...."

#1 and #3 at