Couple suggestions - Before anything else, run an good antivirus on your system. They've been known to cause that kind of behavior. Next most likely, I'd consider a problem with the power supply, or overheating. Next re-install all your hardware drivers and make sure they're the most recent versions. . . . just a couple things I'd check if I had such a symptom. Hope it's something relatively simple - If it's something like a bad memory chip, it could be very elusive to track down.