It seems the culprit on my wife’s iMac (it falls asleep on its own) could be a faulty logic board.

It seems to happen after she has used the computer for several hours straight, and often late at night after a day of fairly heavy on and off usage.

I should note that from day one her 17″ iMac G5 has been making a lot more fan noise than any other iMac I have heard. I thought perhaps it was just that she was overworking the machine and upgraded the memory recently - that did not fix a thing.

I have spoken with the Apple dealer in my area and we will be sending the Mac in for repair. He said:

I believe, based on the symptoms you’ve described, that your iMac G5 has suffered from a typical logic board failure. You would, however, need to bring the unit down for an official diagnosis. The part would then be ordered, if required, and then repaired once it arrives. Turn around time is typically 3 days.

Since the dealer is about a three hour drive each way, we will ship the computer in with a local courier service. Unfortunately, the transit time each way means the repairs could take her iMac away from us for more than one week.

We might have to wait until I finish doing our taxes.