I first had it with the demo, I would start up the game and about 5 seconds after the home screen comes up the monitors turn off. I tried everything but couldn't get them to come back on without restarting the computer. I figured it was a problem with the demo but I get the same thing in the real game, it take longer but still happens. The first time was about 2 hours of playing and the second was 3.5 hours of playing. I don't think it's the card overheating because it stays about 71C. When I play GTA 4 it's about that and I can play forever with out any problems. I looked in event viewer and there weren't any errors around the time the screens went blank. It is the download version I got from amazon. If there is any more information needed just ask.
Thanks,
Kenrevo