Well, have you recently added any hardware? How do your voltages look in the bios? Sometimes, you can have just enough power to run what you have, then adding anything will cause unexplained restarts, because the power supply doesn't have enough power to boot. Also, have you considered buying a harddrive switch? They only cost about $20, and you can run Windows on one drive, and Linux on the other. That way, neither OS has anything to do with the other's operation, ever. I have one. It's pretty cool, because you still have access to the other drive, even though you didn't use it to boot. As a matter of fact, newegg.com has them for $14.99.