Computer restart on Stability test.

[skullmonkey]

My computer started restarting from time to time only when I play League of Legends. I started testings. Test with stress test from Everest and went great for 2:40 hrs. Then tested with Prime95 and went great for 2 hours. Then I started the GPU test with FurMark and checked:
Stability test,
Extreme Burning Mode,
Log GPU Temperature,
Full screen,
1680x1050,
MSAA 8x
Post-Processing

After some time, lets say 1 minute when the temp went only to 85 or so Celsius the monitor turned off but the computer continued working until I shut it down and then powered again.

I'm running
Core2Quad 9550
8GB DDR3
ATI HD4870 1GB ram
550W no name PSU

Someone have thoughts about this problem?

Thanks, skullmonkey.

[Nomicus]

For what it is worth I am having pretty much the exact same issue on my new system.  I can run Prime95, memtest, etc with no issues

However running Furmark or other Graphically intensive programs (Call of Duty 4/5) will cause my video card to shut down. (the monitor goes into standby mode and the PC keeps running or the PC will just shut down.) Furmark can kill my PC in about 30 seconds.  I have been working with Alienware to try and track down the problem. 

Here is what we have done so far:
Tried several different drivers
Reinstalled the OS
Replaced the Video Card
Moved the video card to the other slot.
Reset the bios
etc..

I will be back on the phone with them again tonight.  If we figure it out I will post another update.

My system:

Alienware AX58
6Gb Ram
1000 Watt Power Supply
Zotax GTX 295 Video Card
Vista 64bit

My hunch is that I have a faulty power supply, but I have not been able to convince the tech support people to send me a new one yet.

Good Luck...

[skullmonkey]

In my case was the PS. Changed with Coolermaster 700w Silent PRO and FurMark went for 2hrs with no problems till I shut it down.

[Nomicus]

Thanks for the update, Alienware is sending me a new power supply.  Should have it in a week or so.