PC shutting down randomly

[Nitemare]

Let me explain this before you jump to conclusions.

When I built the PC, all seemed to work well. These are the parts in the PC:

ASUS A8N-SLI Deluxe Motherboard (which I think may be the problem)
Athlon 64 3000+ Venice
Corsair XMS 1GB (2 x 512MB) DDR400
Sapphire Radeon X800 GTO
Western Digital 80GB IDE drive

I am stuck using the old hard drive because, apparently, this motherboard refuses to properly read the SATA hard drive, and thus I cannot install Windows.

AND...since this is likely what many will claim is the issue...

ENERMAX 420W PSU (I doubt this is the issue)

Here is my problem: I turn the PC on, let it start up and it within about five minutes, the computer shuts down. When the problem originated, it only shut down when I did something such as go to a website or start up an Internet program, leading me to believe it was possibly a virus. However, as it turns out, there was no virus. Just to be sure, I wiped the hard drive. Now, when I try to install Windows, guess what happens? The PC shuts itself down before installation is even finished copying the files.

Is it possibly a short? What other scenarios are there? I really need to get this PC up and running for my family.

EDIT: Er...possibly the wrong forum. I came here from a search engine.

[Nitemare]

Ahhh, that reminds me.

There is a huge possibility that the chipset fan is failing to properly work. (It was making weird sounds, and on boot it would inform me it wasn't working. However, those errors have left, and it appeared to be working last I checked. This specific motherboard has had loads of trouble with the chipset fan.)

If that is the case, then the PC would shut itself down? I think I need to hook it up and see how the chipset fan is doing.