It is possible that there is an issue with the CPU. THere was another guy on here in the last week or two that had a Hard drive that was giving him grief. It might have been doing something similar now that I think about it. He replaced his HD and was back on the road.
OK, here is that thread... while not the same, it is an odd one I had never seen before.
viewtopic.php?f=2&t=712
Hopefully you are not watching the death throws of a dying motherboard...