Just joined to post that i'm also experiencing this problem on my brothers ASUS 7850 2GB.
I've found countless threads in other forums and yet to find a solution. I'm on 13.4 and its still not fixed. The system i built for my brother, he complained of this problem and another, i narrowed down the other problem and it appears to be the motherboard. He told me of when the display would goto sleep he would have to reboot it and sometimes would get an error relating to the display driver.
I figured the MOBO problem was just causing this.
However while awaiting for return of his motherboard i've put the 7850 into my system, whiped and installed drivers from AMD for the 7850 and am experiencing black screens after the display being put too sleep.
After awhile of the display being put to sleep, the screen will awake but be black. If i hit CTRL + ALT + DEL it will launch the Win 7 option screen for task manager, log off etc and all is good again.
I'm yet to experience the error message that he received relating to the driver, or having to power down to get a response, but i'm yet to leave it sitting for greater than an hour.
To recreate the problem, i've set display to sleep in 1 minute of no operation.
I will wait about 30+ mins and then go to wake the computer, it will sense input, monitor will awaken but the screen will be black.
This isn't an isolated issue and there are countless threads on the internet relating to this exact issue, and all fingers pointing at "zerocore" being the culprit. Seems to only happen on some cards. The only fix is to disable the display going to sleep all together.
I'm close to RMA'ing it, but wonder if it will just occur again because it seems to be a possible driver issue.