I'm having an interesting problem with Windows 8.1. The computer should be going to sleep on its own (it doesn't always) so I sometimes put it to sleep manually. 75% of the time it works fine, but other times the display will go black yet the computer remains on. If I try to "wake" the computer (i.e. restore the display) nothing happens... the display stays dark while the computer stays on. The only solution is to either power off or reset the computer.

Has anyone else experienced this before? Any idea what might be causing it?