It happened in about 3 stages. I have it set to sleep automatically after 5 minutes of inactivity. It initially refused to wake, then, after changing mouse batteries, it did wake, but a screen flashed by that said it was updating windows. Don't know where that came from. Then died and refused to wake. The power supply would turn on, and fans run, but no HD activity and no screen. Like I said, my PC tech made it come to life but I did not stand and look over his shoulder and so don't know what or how he did it.