After a minute or so, the system just powered off. Pushing the power button had no effect.
I noticed that the fan in the power supply was still spinning. I unplugged the PC, plugged it back in, and the power light came on, fans spun up --- and then it powered down again, again with the power supply fan spinning. It contued to spin for 30-45 seconds.
It remains in that state. The power switch has no effect at all unless the machine is unplugged, then it will provide power for .5 seconds or so.
Enermax EG701AX-VE-SFMA Noisetaker 600W Power Supply
Asus P5WD2 Premium Motherboard
Intel Pentium D Processor 830 3.0 GHz, 800 MHz FSB
ATI Radeon X850 Pro PCI Express
1 Plextor PX-740A 16X DVD R/RW CD-R/RW
1 Western Digital Caviar SE16 WD2500KS 250GB SATA 7200 RPM
1 Western Digital 200GB PATA 7200 RPM
1 3.5" Floppy
Zalman CNPS7700-Cu Coller
2 120mm case fans (Bottom front, top rear)
1 80mm case fan top vent
40mm fan behind each harddisk