Doesn't turn on from the power button at all, suddenly, nothing, nada.
I'm actually dealing with the problem, but I thought I would share it here for any DUer who may experience the same thing, because it seems to be a common event with G5s. My main trouble is I am in Mexico and Apple repair people are scarce. So I sent my computer with a friend on a bus to Guadalajara to the man I bought it from. He is actually very competent, although he wasn't aware of this G5 repair extension program:
http://docs.info.apple.com/article.html?artnum=302181I sent him the link, he read it, checked my serial numbers and found my iMac was eligible. So what could have cost me about $400 in parts and delivery of a new power supply now won't cost me anything. It could still go wrong, of course, I don't have the machine, so I don't know yet, but I have my fingers crossed.