Hi,
I stumbled on this problem a week ago, i checked everything, i even changed the convertors and cables for it. When i open a game it just black screens sometimes not even at 70 degrees just pure black screen from the start. I did a stress test to find out and at 72 degrees black screened me, then i decided to up the power limit to 50 and to get the fans at 100% and it worked wonders, it reached 70 degrees but it was still running. I use a VGA-DVI D convertor and my psu is ATX 600W 20A which should be more then enough for the card. Anything can be useful at this point, beginning to be desperate.