welcome to LQ!
Assuming that you've googled, and haven't come across similar cases and/or
explanations my best bet is faulty hardware. Get a live-cd with memtest
on it and check your RAM.
p.s.: I really assume the above - that is, I didn't try to search
for your problem myself[/edit]
Last edited by Tinkster; 11-09-2009 at 11:33 PM.