Random restart. Windows boots into black screen.

Hello,
Last night I was playing a game, when suddenly the computer just restarted. No error message, nothing. It just restarted. So on the way back to windows, it got passed the BIOS check etc, but after you see the windows load screen, it gave me a black screen with a cursor. Ok, so I tried again, and again with the same result. SOMETIMES it would just restart as soon as windows loaded. Here's the odd thing - I turned the PC off and waited until the next morning. I turned it on, and....it's magically working again? I'm afraid this is going to happen again, anyone have any ideas?

This is a 2 month old system. New Ram, HD, Processor, Mobo, Videocard, everything.

Intel Core 2 DUO 6400 @ 2.13 ghz
2GB Patriot RAM

any ideas are appreciated, thanks.

Did you build it or buy it as is?

If the latter I would consider returning it.

If the former there are many troubleshooting steps.

I suspect from what you describe you had a heat issue somewhere. The blinking cursor is an indication that the system cannot communicate with or find the hard drive.

You can run the manufacturer's diagnostic on the hard drive also run MemTest on the RAM.

Does this only happen during games? Can you force a repeat of the problem?

You can also run Prime95 which will max out your CPU. See what temps you are getting with SpeedFan or CoreTemp.

Another heat source of course would be the Graphics card.