1. Start in safe mode
2. Go to Control Panel -> Administrative Tools -> Event Viewer -> (Left pane) Windows Logs\System.
See if there's anything weird in there regarding failures or something.
I didn't see anything there. And it's not locking up, just restarting. The other weird thing is that when I'm running the GPU folding sometimes the CPU side will get so slow that it will take 30 seconds or so for the cursor to move to match the mouse, and it will remain jumpy for minutes at a time. I'm starting to think the PS is failing under load. It tests good, but of course that isn't under any load at all. I replaced it with a spare PCP&C 750 watt model and am running it for a while to see...