My computer keeps rebooting itself at random intervals

[Nitwon]

I recently installed a 7900GS in my pc (check my rig), since then it has started rebooting at random intervals, sometimes it wont do it for a day or two, then it will start again. I have installed the latest drivers and even tried soem third party ones to no avail. I don't even think it's the graphics card's fault since it did the ame with a 7600GS i've used before.

I know what it isn't:
-Not overheating, (cpu:35-45, system:25-35, gpu:50-65 degrees celcius) before anyone says it, no, 65 degrees is not overheating, it's slowdown threshhold is 130. (someone on yahoo answers told me it was too hot lol).
-Not the PSU, I've tried several, and the one I'm using now has powered much better stuff in the past.
-Not the driver (i think)
-Not overclocking problems (i overclocked my cpu once but that was before installing the gpu)

I've had people say that it's the motherboard and/or cpu, but i don't really have any way of finding out.

It even restarted on its own once or twice when using the on-board graphics, but very very rarely, more often when using a powerful gpu.

Any help?

[notsobig]

So looks like there's one thing you haven't checked yet, which is memory. And bad memory can randomly reboot your pc like that. I think you should get yourself a copy of memtest86 and check your memory throughly. That's probably where I start troubleshooting if I was you. BTW welcome to the forums.

[iranu]

Welcome, can you do the following for us please.

Right click "My Computer" icon, select Properties, click the "Advanced" tab, click the settings button under "Startup and Recovery", Under "System failure" uncheck the box marked "Automatically restart.

This will stop the PC rebooting when you have the crash and instead will display a blue screen (of death) or BSOD. This will give you information about what is causing the crash. Next time you have a crash write down what the error says and then you can post it here or google it.

Ram faults tend to cause random crashes so if you are getting all sorts of BSOD errors then the ram will be the prime suspect. Do as notsobig says and run memtest. You may also wnat to look at the fsb/ram divider you are running and ram timings if you are overclocked.

[Tetras]

when using the on-board graphics, but very very rarely, more often when using a powerful gpu.

I assume that means it rarely reboots when pottering about in Windows, only when gaming?

Is the Neopower what you are using now? How old is it? (yes I know you have tried different PSUs but humour me )

[Dingo]

System specs would be good!!.

Have had a similar problem with a 6600GT and it turned out to be a heat problem.........side of case off no problem but with side attached major problems within gaming.

Resolved with additional fan over Northbridge on a DFI NF4 board.