I have a same or similar problem.
It happens when i have the "Turn off the display" set to any amount of minutes. When the monitor screen turns off and then when i try to wake it up the monitor doesn't want to turn on. I also have the sleep mode and hibernation disabled. It also happens when i run 3D Mark Vantage when it finishes the benchmark it only has the black screen on the monitor at the end.
What i do to get it to work is disconnect and reconnect the hdmi or dvi connector from the video card only after i do that it comes back to desktop screen.
My setup is Asus Rampage Extreme IV with 3960X, Corsair 240gb ssd, with two Sapphire HD 7970 and 27' Hanns G monitor.
We both have Sapphire brand...
I thought that this was a driver problem at first but after 6-7 driver updates i still have the same problem.
I also have 3 Sapphire HD6950 and i dont have that problem.
What monitor do you have??