PSU Problem?

Hello Everyone!

So I have a computer that I put together ROUGHLY two years ago, and I have started using it again after being away for a year.

The components:

-M3A78-CM Motherboard
-AMD Athlon II processor (I think that's it - it's certainly amd duo core 2.8ghz)
-8400gs silent
-2x 4gb ddr2 ram (only shows up as 2x 2gb no matter how many times i update bios, configure according to motherboard's manual etc. - and it have w7 pro 64 but whatever)
- 500w power supply (RP-500-PCAR 500W ATX12V)
- hard drives, WD Caviar or something


THE PROBLEM:

The 8400gs silent was the last thing to be updated in the computer, everything seemed to be working fine until last night.

I was working on some video editing (using two monitors, if that's of any importance) and some 3D work and the computer froze/hung - i couldn't move the mouse nor did ctrl-alt-delete work at all - totally unresponsive. So I turned of the computer using the power supply switch then flicked it back on and tried to use the power switch connected to the mother board to turn it back on. The power switch did nothing. Upon inspection I see that the motherboard light is on but hitting the power switch doesn't do anything at all. I kept removing components and trying - eventually I got to the power supply just plugged into the motherboard (granted the cpu was still in) with still no result.

I removed the mobo's battery and left it out all night, and in the morning I tried it again with no result, tried a different battery with no result and tried using the jumpers as described by the motherboard's manual to reset the bios or cmos or whatever with no luck.

This morning I also tried plugging in the power supply to another mobo to test it out. It wasn't really the best experiment ever, as there could be an compatibility issue between the CPU and the mobo I was testing it with but this is what the PSU was doing:

http://www.youtube.com/watch?v=pRezR4fe-Pw&feature=yout...

You see it at about 6 seconds - the best way i can describe it is that the fan was like a clock, it would tick and move very slightly pretty much every second.

Any insight to this is appreciated. I'm extremely broke and am (was) relying on this computer to do editing jobs and I really hope I don't need to sell something (or myself) for new components  

*Also i tried getting dust out of everything with compressed air, unfortunately I am not manly enough to open the psu box and get my hands dirty/electrocuted.