AMD QuadCore Phenom in an Asus M3N-HT Deluxe using the onboard graphics.
I had difficulties installing Ubuntu 12.04.4, the GUI wouldn't come on. After some poking around, it turns out that re-installing WITHOUT allowing the download of updates or 3rd-party things solved the issue.
After a successful login, I performed a complete system update and rebooted, and everything is still fine.
Prolly a 3rd-party driver that isn't really compatible with the hardware, or that wasn't setup properly, or whatever.
Hope this helps somebody somewhere some time.