iMac or screen goes to sleep or seems to

I see other similar threads starting to show up, as if this issue was a time bomb waiting to go off once these systems got over 6 months old.

My system still works perfectly fine in Windows, but if I try to run OSX (which is fully patched) it will die from anywhere within 30 seconds to 30 minutes of use.

Going to cross link this thread with one of the newer ones, so people will start to see the issue is getting more prevalent.

Well, it seems that wiping the drive and installing a fresh OS has done the trick. It's been 10 days with heavy use and the issue has not repeated itself. I know it's a hassle but you may want to give it a shot.

This is happening to my 1 week old 21 inch iMac with the base system specs. It's been fine the whole time except for today when it started flickering and the screen going into sleep. It's hard to revive, it doesn't show anything sometimes after I've put it in sleep or restarted it. I tried downloading the 27 inch firmware fix but it wouldn't let me. Any help?

Same issue on my 2 week old 27". Reset smc and zapped pram. i am hoping this will help.It seems there are other users experiencing this issue in various forms. I will monitor this forum for any updates on this issue.

Thanks /nick, I'm glad to hear that wiping your drive was an option for you and that it worked. It does further indicate if not now proove the problem is a software problem in OSX. I may try to install a fresh copy of OSX to an external drive as you first did to test the theory, then maybe wipe my drive, but it's really not a great option for me and my Windows partition is still working fine. I'll probably just wait for Apple to finally figure out what the software problem is and release a fix, assuming that will eventually happen. I hope yours continues to work perfectly, but if it does act up again please let us know as that could change the dynamic of the issue. Thanks again!

Same problem - 2 week old 21-inch. Have had to do SMC Reset at least a dozen times now. The screen will go black but the iMac is still running. Space bar doesn't do anything, sometimes quickly pressing the power button will turn the monitor back on... but usually the whole thing has to be turned off, power unplugged, SMC reset, plug power back in, and turn on. And even then I don't always get an image. Hearing the sound, but no picture.
Just a little bit frustrating on a brand new computer.

I get the blackout without the restarts and tried all the suggested remedies on these forums with no relief. I can see light from the grill covering the ram access port so I do not think it is fully shutdown but will not respond to any wireless input devices so I must press the power bottom on the back to restart It which it does in a normal fashion. The machine does not seem to be running hot (much cooler than my black Mackbook) . I guess I will be bringing it in but I do not feel optimistic given the posts by users who did so and did not get a fix. I think this issue will take some time to resolve. I just wanted to add my two cents.
See Berry's list of similar posts as follows:
27-inch / 27" iMac Random Shut down:
http://discussions.apple.com/thread.jspa?messageID=11791328#11791328

Random Restarts on Intel based iMac
http://discussions.apple.com/thread.jspa?threadID=1943134&start=0&tstart=0

Sudden restarts and shutdowns on iMac
http://discussions.apple.com/thread.jspa?threadID=1865839&start=0&tstart=0

And this current one here: 27" Core i7 iMac blacks out then restarts itself for no reason:
http://discussions.apple.com/thread.jspa?threadID=2258132&start=0&tstart=0