Asus P5N-D OEM not booting.

[Herpderp23]

Hey. I'm trying to fix my brothers computer. He had an NF51 motherboard before, but the capacitors blew out so we ordered an OEM Asus P5N-D on Newegg. Computer was not booting inside the case, so I've pulled it out and I have it laying on a cardboard box to ground it out. Everytime I turn it on, I get to bios but after a few seconds it just shuts off. I can't get it to run any longer than 15-20 seconds after turning it on. All wires are firmly and properly connected and I've checked many times. I've tried 3 diff sticks of ram, and even re-applied the paste on the processor and heatsink. Reset jumpers, and even pulled 1 part at a time out to see what it could be, besides the PSU. Could it be the motherboard which is OEM, or could it be the PSU? Everything is from the build he had before, except the motherboard which is newer. I"ll post specs below, and hopefully get some help lol. thanks =P

Asus OEM P5N-D Sli mobo
Pentium D 3.0ghz with Stock HSF
Evga 7900GT
WD 250g HD
And some piece of junk PSU EosSmart or AthenPower..i dont even know exactly which it is. rofl.

 

[Atomic Rooster]

Is the CPU fan plugged into the correct header?

 

[Herpderp23]

Yup.

 

[Mulholland]

I would try a another PSU.

Maybe it was the PSU that damaged the origional Motherboard

 

[Whyfly??]

It sounds like a fan problem, like an overheating problem.
I don't see how a PSU would shut off after 15 seconds every time.