Rev A iMac - 233MHz, 32MB RAM, 4GB HD (this is a stock machine - not my hacked iMac I have referred to in the past)
Symptoms: when plugged in after sitting for some time, the machine gives a good chime and the power light is green, then a loud click and it shuts off completely. The moniutor never turns on. The machine will not repower on, even if the CUDA is reset unless the machine sits unplugged for some time (a few hours) and the CUDA is reset prior to power on. On some occassions the machine powers up, with the yellow and green lit at the same time and just sits there (no monitor, no chime), just fan, spinning drives - no real life. Hitting the reset button at this point throws me back to the green light, chime and then off again.
I have not tried swapping the mobo with my other iMac yet, but have the option on hand to try. The hesitation is I do not want to infect/jinx my other iMac that I have finally got working again.
Any ideas on what the problem is? My first thought is the analogue board, but I am uncertain if it is this or not. I am hoping that this sounds painfully familiar to others.