Another busy weekend (my dog's dying), but I made some time to take my PC apart. I unplugged all the drive cables, from both the drives and the mobo, and took them out. I took all the cards out -- video, sound, ethernet, and modem. I took all the RAM out -- PC133, 2 DIMM's of 128MB each that came with the computer, and 2 DIMM's of Corsair 256MB that I later added years ago. I even took the brain out -- the CPU and heatsink and fan is all on a card of its own, that plugs into a slot in the mobo. I unplugged the cables to the case reset button and HDD LED's etc. The only thing I currently have plugged in to the mobo is the ATX power cable from PS to mobo, and the connector between the mobo's power-on pins and the case's power button. I.e. the minimal # of connections to still be able to turn it on. And I unplugged and replugged-in both. I also brushed out with a small and very soft paintbrush any dust on the boards and on any pins and in any part of any of the slots. Same deal, the PS fan spins up, it runs for about two and half seconds and then quietly shuts off. No click sound, like when I do the Windows shutdown and it shuts itself off. Instead, it sounds like it might if it just got unplugged or something. I even tried a different power cord.
To quickly answer the remaining questions from the last JE, I had vacuumed with a plastic attachment, and hopefully plastic's not capable of transferring electrostatic charge. (And it's summertime and humid, so *I'm* not zapping anything, at least as far as I notice.) And it's not running XP, it's the Windows 2000 Professional SP4 system that's been stable for forever. (And I don't use automatic updates from MS, I go to the technet section of MS's site and review them first and apply them manually, and I haven't updated in months (I'm behind).)
So, about all I have left I think are the main board, the power supply, and the CMOS battery -- everything else has been taken out.
And the two events of note, as far as I can think of, that coincided with the thing breaking, are unplugged for several hours, and vacuumed out.
The world wide intertubes seem to think that a failed or failing battery wouldn't prevent a boot. But corrupted CMOS data might. I'll try shorting the pins that reset the CMOS data. I think if the battery is dead it would still boot, and maybe just have to rediscover all the H/W parameters again?
Can a power supply be "dead" when it still starts up? My only (limited) experience with dead PS's is that they don't start up at all. (One even made a loud snapping sound and spat sparks at me, and a really strong smell, before it ceased powering up -- startled the crap outta me at work.)
And I'm hoping that the main board didn't just decide to die, or rather, some part of it -- it still spun up hard drives when connected, and the CPU fan, and LED's, etc.
So, with this narrowed down some more, anyone have any hunches? I figure a battery's pretty cheap, but I don't want to buy a new power supply (if I can still even get one for this thing -- a 230 W for an ATX board with it looks like some 3.3V and some 5V and some 12V lines, circa April of 2000) if it's doubtful that that's it. Any advisement is deeply appreciated -- I'm just a programmer so this stuff is not my area of expertise.