My 18 month old Rev A G5 iMac was stone dead yesterday morning when I tried to wake it. No lights, no noises, no sign of life at all, so probably a power supply failure. It's obviously out of warranty and I didn't buy Applecare so I took it to the local Apple store genius bar for their verdict and they also thought it was most likely a power supply. They called me back this morning (less than 24 hours) having fixed it with a new power supply. There was no charge for this fix as there is an extended free replacement program covering this part. So kudos to Apple and the Tigard store geniuses for a good support experience.