robucf4,
Did you do memtest?
If not, grab memtest v1.70, and run test 5, for at least an hour, on each stick of RAM individually in each slot.
If there are errors, take out that stick and put it to one side and try the next one.
I honestly havent come accross your problem before, so I am just going through a process of elimination.
It could always be a faulty CPU, or PSU as well, but check the RAM first