HP laptop sudden shutdown, no gui sessions

[Ralph Pichie]

I have a dual boot HP 620 laptop running Win 7 and Ubuntu Natty. Today
I had 3 sudden shutdowns within a few minutes, this time while
connected to AC power. After the third, I am unable to start an X
session. I've dropped to root and tried from there. Tried fixing
broken packages. Tried reconfiguring xorg and gdm. No luck. Any ideas
short of grabbing my files and doing a reinstall?