iMac 27" Black Screen?

Mine turned out to be a software issue. Machine would boot up, could hear the hard disk. Screen stayed completely black. Went to Radio Shack to pick up an adapter, hooked up antother monitor, it worked - so - whew! - it isn't the graphics card.

Main screen had been down for two days. After hybernating - it came back to life. I had the display back. Soooo... it was a software issue. Lion has been sort of dicey with hybernation from day one... I thought about attemting to find and replace faulty Kext files - but who's got time to dig around and find out where the issues are. Shouldn't Apple be doing this?

I upgraded to Maverics, and bingo! No more dicey hybernation. No more black screen. Issue solved.

I diagnosed this as a short in my keyboard - thanks to someone mentioning the keyboard as a possibility. My keyboard was sending out the key combination to toggle displays on a whim (alt+cmd+eject.) Whenever this would happen the main display would toggle off. Later on, on a whim once more, the keyboard would once again send alt+cmd+eject, the short would temporarily resolve and the main display would remain on for a period of time - until the next time... Replacing the keyboard absolutely fixed the problem.

I had downloaded a Sierra update and then plugged the charger cord into my keyboard. When I pulled the cord from the keyboard, everything went dark. This was yesterday. I then shut the iMac down. This morning I tried to log on but the screen had darkened more and was almost pitch black. Looking for an answer on my IPad, I found several suggestions Here. What worked for me was clicking on Preferences, Displays, and screen settings. Somehow the button for brightness had been turned to off. Also, I removed the option for automatically setting the brightness and I set it at my discretion. Hope this works for others.

I'm having the same issue recently (older iMac 27, Mountain Lion), though the iMac does not really go to sleep. It's only the screen that turns itself off randomnly, the Mac is still awake. To get it back on, I use the key combination alt-cmd-eject to actually put the iMac to sleep. Hitting any key will wake it up with the screen turned on again. Annoying. Can't find an answer so far as to where the problem is coming from.

I replied in another thread but it applies here as well. I think it could be the keyboard.

I had the problem recur 3 times exactly the same, screen goes dark, computer is still on as the audio works. Twice the genius bar failed to find the problem.

Then I realized they use their own keyboard when I take it in. The keyboard has a brightness control, so it's not completely illogical.

I have a new keyboead and so far the problem has not recurred.

I turned my keyboard off... Mac has been running fine now for 6 hours

Keeping my fingers crossed

I think we have a winner... How can a keyboard cause so much graphic problems ?

The bigger question is why hasn't Apple figured it out yet?

I'm on day three with the alternate keuboard, no repeat of the problem. I'm going to have to use this one for a couple weeks and if the problem doesn't recur, get a new keyboard (this one is klunky). Please do let me know how your experience progresses. I appreciate it.

Are you using another Bluetooth key or USB?

6hrs and still good, was crashing every 15 mins before

Hope Apple figures this one out soon... I don't have another keyboard

Guess I'll go buy one later... 3 days is pretty good ...