Welcome to seven forums: Looks like an overheating problem. I would first try some canned compressed air and blow out the exhaust and intakes. Of course after the system has been shut down to cool down. But as bad as it is it could be a bad card,make sure yo have all the latest
drivers. But since this appears after a couple of hours i would hedge a bet it is overheating, which may have caused your card to go bad as well. My opinion. fabe