Problems in multiple OSs implies hardware. It could be a problem with the card, or elsewhere. The likely candidates to my mind are, in no particular order, faulty graphics RAM, blown capacitor, intermittent short or voltage spike. Check all over for blown caps (they'll look domed, cracked or have goo coming out of them) and check your motherboard stand-offs (the bits that keep the motherboard appropriately electrically connected to the case). Give it a good clean with compressed air in case you've got something conductive in there (using screws on cheap cases can fill the computer with little metallic ribbons which can cause all sorts of havoc. If you have a spare PSU you can swap in then that will help identify a potential cause.