I got a new VGA, because my 8800GTX died. We bought an Sapphire HD5670 with 512mb GDDR5 memory. It's not a used VGA, it's completely new. When i start my comp, and the Windows boots (Vista Ultimate SP2), it doesn't have any problem. But after some hours (not playing, just surfing the net, etc.), the screen gets dark, sometimes it shows some bars, and not alltime, but sometimes the computer freezes completely. Yesterday, i could play games without problems, but today it started to freeze in games too. I thought, that it had an OpenGL problem, because it stopped working, when i was using some OpenGL based software. But the internet is not OpenGL based, i guess... So today it started to freeze in Direct3D games (and black screen, bars, etc.). What can be the problem?