IMac Screen goes Black
Screen on IMac goes black (just like it went to sleep) all of a sudden and the only way to get it back on is by hitting the power button. When the computer sleeps, it will wake by tapping the space bar twice but when it goes black, this doesn't work. After hitting the power button, the computer will go right back to the screen you were on prior to it going black, nothing is lost and it doesn't have to re-boot. This started out happening once in a while like maybe once every couple of months, then maybe a couple of weeks, (didn't really pay attention to time frame) now it has happened twice today. Does anyone have any idea's or suggestions on what may be causing this? I have not noticed any particular application that was running when it occurs. Any help would be apprecaited, thank you in advance.
Mike
21.5 Mid 2011
Mountain Lion
Version 10.8.2
2.5 Ghz Intel Core i5
4 GB 1333 MHz DDR3
Graphics AMD Radeon HD 6750M 512 MB
iMac (21.5-inch Mid 2011), OS X Mountain Lion (10.8.2)