iMac screen won't turn back on after a sleep session in Windows 8.1
I have a 2011 iMac which I have been having the same issue with since windows 8.  For me, it is an issue with when "turn off the display after..." is set. I have turned off this feature, and my PC just goes into sleep mode instead. It is slightly inconvenient though, as I can't run things in the background during.