Just recently my Radeon 4890 has become unusable. It will boot to windows and look just fine but after about 5 minutes it the screen will become a bunch of artifacts and will either lock up or go to a bsod giving an IRQ error and then lock up. When I take the card out the computer works just fine. I've used two different diagnostic programs and the temperature of the card is locked at negative 163c. I've thoroughly cleaned the card of all dust. It was very dirty when the problem began. Did a temperature sensor on the card fry causing it to malfunction? Any help would be appreciated.