Computer Won't Turn On...Usually

[Foxoq]

Alright, I have been having this weird problem with my computer the past while, but it's starting to get worse. Basically, it works great, as long as it's running. Here are the specs.

AMD Athlon 64 X2 4400
DFI LANParty UT NF4 Ultra-D Mobo
2 x 1GB DDR400
eVGA nVidia 8800 GTX
Antec Neo HE550
Samsung Spinpoint P 200GB SATA2 HD
Windows Vista Ultimate


However, as soon as I turn it off, the little Standby Power LED starts blinking like some computers do when they go into sleep mode, even though I have sleep mode disabled on this machine. Attempting to push the external power button does nothing, and neither does the internal one mounted on the board. I used to be able to unplug the machine, wait for the light to stop blinking, and plug it back in, but now I have to unplug it or flip the PS power switch on the back of the machine and leave it for five or so hours before it will turn on for me again.

The thing is, when its on it runs great and I can leave it on indefinitely without problems, its just as soon as it goes off there is a problem. I think this rules out most hardware problems. I have tried unplugging and replugging the power cables, to no avail. Should I try resetting the CMOS?

 

[Foxoq]

OK, I pulled eveything out, and began reconnecting things one at a time to see if I could isolate the problem.

With everything out, except for the CPU and fans, and everything unplugged except for the power cables, the light came on as a solid yellow. (The way it's supposed to, the way it does when it turns on.) However, with the RAM seated, the light began flashing again. I tried switching the slots the RAM is in, but the problem still persisted. I even tried fiddling with the DRAM voltage select jumpers on my board, to see if that would do anything, but still nothing. (I know I have switched them before when I had this problem and it fixed it, but now it does nothing.)

The funny thing is, the RAM works fine when the computer is running, as does the mobo. What possibly could be the problem?!

 

[SolMiester]

PSU?

 

[Foxoq]

But the computer does work, so therefore it must be getting power when it turns on?

I guess it could be shorting or something..

 

[Foxoq]

Alright, things get weirder. Everything is fine with one stick of RAM in the system. It doesn't matter which stick in particular, or which slot it is in, it just has to be one. As soon as I plop the next stick in, the light flashes again and the system refuses to turn on. Again, it doesn't matter where I put the second piece, or which stick of RAM is the second piece.

Arrgh.