Problems with my new 6950, computer getting stuck or restarting, please help?

[dreamer2008]

I bought a new HD 6950 and put it to work at mining. But I encountered several problems. First, when its mining and I try to put a youtube video, the PC freezes. I am almost certain that this is related to the 98% usage of the video card while mining. Edit: I found out that this related to the flash hardware acceleration.

But the problem that worries me is that the PC restarted a few minutes ago without any error or warning, without even using it. I was in another room at the time so I didn't see what was going on. The temperature of the card was a steady 65C, so okay. Is there any way to check why it restarted? I am using Win7. I didn't see any error message when the system restarted.

The PC was left alone to do mining for about 14 hours with no problems. I am using guiminer.

I didn't overclock the card and I don't want to do it.  

[Dale]

What kind of power supply do you have? I'm talking about manufacturer's name and its power capacity.

[dreamer2008]

Thermaltake 500W

Edit: It seems I might be safe. The PC didn't restart again and it was open for more than 48 hours.