Sysytem went from Great to not Even Powering Up?

Well I'm at a complete loss on this one. I'm not overclocking anything at the moment beyond my Video Card, and I have no real idea where to turn to on this question. Hopefully you guys have some imput as to what is going on with my system.

System Specs

Athlon 64 3000+ 939
Chaintech Nforce4 Ultra Motherboard
Gigabyte Nvidia 6600gt PCI-Express Video Card
Corsair 512mb X 2 Value Ram, PC3200
Samsung 120gb SATA HD
Xaser III Lanfire Case w/ Thermaltake 420w PSU
NEC 16x double layer DVD RW Optical Drive
Artic Cooling Freezer 64 Cooler

The Problem

So I put this computer together and it has been working fine for almost 3 weeks. I mean flawlessly, it was beautiful. Suddenly today I started getting Blue Screen PFN_List_Corrupt errors. I haven't changed anything, I didn't upload any new drivers or download anything strange, so the first thing I thought of was a memory error of some type.

It's happened before on other computers, no big deal. So I start up my computer and go to look online for a bit to check out my warranty information to prepare to possibly send my memory back for a new set when I get another Blue Screen Error. Alright I figure...two in a row. I go to turn on my computer again, it won't POST Did something happen to the BIOS I wonder? So I turn everything off and unplug it and go to reset the BIOS with the Jumper like I've done in the past.

I plug everything back in and prepare to turn it back on and...it won't even power up! What on earth happened? Did the memory AND the PSU go bad or something? I've never had this happen before, where a memory wouldn't even power up. Sometimes if I hit the power button, the system flashes for about a millasecond, and then nothing. Nothing was moved, nothing was taken out, all of the cords seem to be connected correctly to and from the PSU. Does anyone have any idea what might cause this problem? If anyone has any suggestions or ideas, please let me know. I[m on my spare computer now while my poor baby sits in silence.

Sounds like power supply death. Do you have another to try out?

Unfortunately I don't think I have any good PSU's to try out. Would a dying power supply cause those memory errors at first? I have some old school PSU's (like 3 and 4 years ago), but I'm not sure if they'll handle a PC like this, I'll give it a try though...if they have enough connectors even that is.

Quick update-

So I unplugged the PSU from the surge protector and plugged the computer directly into the wall socket, and reset the PSU. Now I can seem to get power, but it's a real crapshoot. Sometimes the power flickers for a bit, I can see the LED's on the computer straining, sometimes I get no power, and sometimes it powers up but it won't even POST on any of those senario's, at best the fans will just spin and it will sit there doing nothing. I tried again resetting the BIOS to see if that would do anything, and nothing.

Maybe it is the PSU. While my computer knowledge is limited, I can't think of anything else that would have these distinct types of problems.

Sounds like a PSU problem... you said you have some old PSUs, I'd suggest taking out all power sucking components (graphics card, sound card, fans, lights, extra hard drives) and trying to run it off one of them. More than likely it IS a psu problem.

Well you've got to have a graphics card in there and I'm betting you don't have a bunch of alternative PCI-E cards to try out. Any friends with decent systems and PSU's to match?

No, no friends with systems like this, I think I'm pretty much alone here.

What kind of load does the 6600GT create? I'm almost certain you have a croaked PSU on your hands, I wouldn't care to risk trying the PSU out on another system unless I was desperate or didn't care much about the test system, but perhaps you wouldn't mind that alternative, assuming of course you have another system to try the suspect PSU out in.

When you turn on the system do you see the hsk fan spinning?
Also what watt is your older psu?