I have a Power Mac G4 (Single 1.25 GHz) that will only sleep the monitor since 10.3.9. If you put the tower itself to sleep it won't wake up without a hard reset. I isolated it down to the external USB Zip 250 drive and it remains unplugged. I then updated this Power Mac G4 to 10.4.6 and now after 24-48 hours, the weekend, it won't wake from sleep on Monday morning. It has been told not to sleep the tower but only the monitor. If I leave it overnight on Monday it'll wake up just fine on Tuesday and for the rest of the week until the weekend and following Monday. I only have the monitor plugged in, Ethernet, and the USB hub in my Dell 20" LCD. I don't plug in the Zip drive unless I need it. It doesn't have any upgrade cards or Bluetooth adapters.