I'm not entirely sure how long my iMac has been doing this, maybe two weeks? When I try to wake it from sleep, the screen does not turn on. At all. At first I thought this was because my mouse and keyboard might not be functioning correctly, naturally the only remedy was to turn the computer off with the power button and to restart it (which took an abnormally long time). Today I remote connected with Back to my Mac screen sharing and it did not turn on either. I know it was awake because when I pressed the brightness buttons on the keyboard, it responded on my MBA's view of the screen. Normally, Back to my Mac does turn the screen back on. Any suggestions? Anyone else have the same problem? It doesn't seem to matter WHEN it goes to sleep either. I've tried resetting the PRAM already and no dice.