Video/sound cutting out all the time.

Hey all. My computer has been acting up of late. I'll describe the progression of the problem.

A while ago while messing around on the internet and watching some youtube videos it lost sound and my monitor went black simultaneously and it said something along the lines of "No input found". I reset the computer and it ran ok for a while but then the same thing happened. I switched out monitors and the issue would still occur, so it's not my monitor I'm pretty sure. I asked my more tech-savvy friends what to do and they said next course of action was to check if it was a software or a hardware problem. I left the bios running for a couple of hours, then ran Sabayon Linux off a cd on it overnight. The issue didn't occur so I was pretty sure it was a software problem. So I began reformatting and it crapped out mid-format. Earlier while preparing to put in the windows CD it crapped out in the Bios also.

So I'm told that it's probably not a software problem and is most likely a motherboard or possibly power supply issue. The issue takes the form of my monitor going black with a no input message and I lose sound so I can only assume other things have gone wrong. The fans still run after this issue occurs however. I have to reset the computer to get anywher after it happens. It runs fine for a short while before the issue happens again. It happens sporadically and I could sometimes log in to windows for a brief period before it dies. That was before the reformatting attempt though, since I deleted the partition I assume I can't do that anymore till I get this resolved and am able to have it up long enough for a reformat.

So I guess my questions are what exactly is wrong? and What should I do? I'll be around to give any information I can. Thanks in advance.

Specs:
Processor: Intel(R) Core(TM)2 CPU 6300 @ 1.86GHz (2 CPUs)
Graphics card: NVIDIA GeForce 7900 GS
Motherboard: MSI P6N SLI-FI
Power supply: 500w, It's a raidmax, I can copy the model number if need be.