BleepingComputer.com: Computer won't Post

I've had my current system for about four years and it's been working fine. Until one night, while watching Hulu, everything goes black. The monitor was on, but nothing was being displayed, no sound was coming, and the system was completely unresponsive. I forced a power down. Now, whenever I turn the computer on, the fans spin up and then, soon after, the system shuts off. I don't even make it to BIOS.

I have a feeling it's my Mobo but I can't see anything wrong with it. It could be the PSU. RAM and GPU have been eliminated as culprits.

So, first of all, does anyone have any ideas as to what this could be?

Second, if it IS my mobo, given that my optical drives are dying, I need another HD, and my case has seen better days ... is there anyway for me to just get a barebones kit and upgrade everything all at once while still retaining my windows installation? Yes, I do have a XP Installation CD.

Thanks guys!
Ben

Specs:
BioStar N4SLI-A9
AMD 64 3700+
EVGA GeForce 8800 GT 512MB PCIe
G. Skill 1GB DDR x2
Antec 550 Watt Modular Power Supply (Don't know the model)

It sounds like the power supply went & took the motherboard with it.
A bad power supply can still make the fans spin & appear to work.
I would not use that power supply with another motherboard.
I would espect it would immediatly fry another motherboard too .

What brand is the computer ?

I got it from CyberpowerPC.

If we think the PSU is gone, I've got nothing against picking a new one up and seeing if that fixes the issue. If I need to do the motherboard as well, that's fine as I've wanted to pick up a new MoBo and a new CPU for some time. Do you think that I could do the MoBo and CPU upgrade at the same time or would windows seriously flip out if I tried that?

Thanks!
-Ben