So I leave my iMac on and it goes to sleep like normal. problem is that I come back and click on my magic mouse pad and....nothing happens. So I click on the keyboard and ....nothing happens, just the black screen. I tap the power button and nothing happens. So I just hold down the power button for a hard shut down and I can hear when it final shuts down. Wait a little while then power it back up and everything is fine. This has happened probably once per week over the last month or so. I can't trace this to anything specific, but I have owned the iMac since September and I think this only started after I downloaded the Facetime beta release from apple directly. Help?!