Computer Build: System shuts off seconds after turning on

Trying to piece together old parts of a computer that has been sitting around before buying a new computer.

There have been some problems with the build but I finally got it up and running and was installing the new OS and the computer shuts off after being on for ~10 min. Now whenever I try to turn it on all the fans start spinning for a few seconds and then the system stops.

I can hear the HD start working until the system shuts down, also no beeps are made and there is nothing that shows up on the monitor. I've checked the connections multiple times as well as assembling/reassembling the comp.

I also cleaned and reapplied thermal paste to cpu, same result. As well as using another cpu I bought (assuming it worked upon arriving), same result.

Searching around I've seen others with this problem but none seem to help. I'm just a bit lost as to whats going on and how to troubleshoot/solve it.


Computer Specs:
CPU: AMD athlon 64 x2 Dual core 6000+ 3.1Ghz (used to work)
Mobo: Asus M2N68-VM (used to work)
GPU: HIS HD2900XT2x Dual LinkDVI VIVO 512 MB 512-bit GDDR3 (Don't know if worked)
PSU: Antec Earthwatts 750 w (new)
HDD: WD Black 1 TB (new)
1 g DDR2 800 ram (used to work)

Thanks in advance for any help.