IMac will not power up!  Help!

I have an iMac that for some reason will not power up, at all.
The specs are: 800 MHz, iMac G4, 512 MB.
It stopped detecting the available WiFi network in my home regardless of where I located it. So I rest PRAM, and no change. I reset NVRAM and all in open firmware, no change. Pulled the RAM and AirPort card and reseated; no change.
So I reset the PMU (pushed it quickly and only once) and now it will not start up at all. No fan. No lights. Nothing.
I don't have any extra plugged into the iMac now. I pulled the RAM and Airport card and have tried booting with and without just the keyboard plugged in.
I've unplugged it and let it set for over 24 hours and still nothing. I have noticed that when I plug it in, the overhead incandescent bench light on the same circuit dims or flickers ever so slightly for a very brief moment.
So I'm leaning towards one of the following:
1. PMU crash meaning I need to replace the logic board
2. Fried logic board which is likely why the Airport card stopped responding (which, by the way, was somewhat intermitant at first)
3. PMU crash that can somehow miraculously be reset saving me from having to get a replacement logic board
4. Bad battery (haven't checked this yet as it seems the machine would show some sign of life if it had a bad battery. This thing is lifeless).

Hello slee:
You have, IMHO, analyzed the problem. I think it is time to take the computer to either an Apple store or to an Apple certified repair shop for diagnosis. I do not think you want to begin replacing things that may be OK.
Barry

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