I've had a white 24" iMac since they came out. It's been great. However recently it's developed a sleeping disorder. I generally leave it on all the time, but have it sleep on periods of inactivity through the power management preference pane. This has been working fine until recently. Now it just turns the monitor off but stays awake. I can click on the apple menu and choose sleep and it's fine. But if it's left unattended - say its downloading stuff or whatever, or we forget to put it to sleep, then it just stays on forever. The fact that it sleeps if I manually intervene suggests it is not related to any connected device, however to rule that out I unplugged everything, even the ethernet cable. Still no sleep. I ran a software update to make sure I had everything. Still no sleep. I reset the SMC and SMU and PRAM. Still no sleep. I booted up in Safe Mode. Still no sleep. I logged out so no users were logged in at all and left it sitting on the login screen. Still no sleep. I click the sleep menu item in the Apple Menu, or on the login screen, or press the power button, and it sleeps. So something in the inactivity check is preventing it from sleeping. Something that runs even if I'm not logged in. Something that runs, even from booting in safe mode. Any ideas. Please.