My 20" iMac G5 (2.0 GHz, 512 MB RAM (stock), AE+BT, Apple Keyboard/Mouse, HP DeskJet 5740) will not sleep! Ever. It's very frustrating. The only nonApple add-on I have is my printer. I've tried unplugging it to no avail. I guess I could try unplugging the KB and Mouse, but I'd have to plug them back in to wake it up. My free AppleCare expires in August.