Hi guys, my first post here 
I have an iMac from 2011 and the serial number matches too (DHJQ). I've no problems with graphics, but:
About two weeks ago my iMac went suddenly off (I wanted to change an address in the contacts app) and it didn't come back. I had to let it off for about 12 hours, after that I was able to turn it on again. I could work for about 4 hours then the iMac went off again (while browsing internet using Safari) and again I had to wait for a longer time before I could turn it on. The problem happened several times.
I ran the disk utility and got a few errors (volume and permission errors). These errors could be repaired and didn't come back. Since then the shut off problem has gone away.
So, is it possible that some volume or permission errors can switch off the iMac (like pulling out the plug) or is this a hint for an upcoming faulty graphics card? Or even something else like logic board or power supply? No ACPP
I have an iMac from 2011 and the serial number matches too (DHJQ). I've no problems with graphics, but:
About two weeks ago my iMac went suddenly off (I wanted to change an address in the contacts app) and it didn't come back. I had to let it off for about 12 hours, after that I was able to turn it on again. I could work for about 4 hours then the iMac went off again (while browsing internet using Safari) and again I had to wait for a longer time before I could turn it on. The problem happened several times.
I ran the disk utility and got a few errors (volume and permission errors). These errors could be repaired and didn't come back. Since then the shut off problem has gone away.
So, is it possible that some volume or permission errors can switch off the iMac (like pulling out the plug) or is this a hint for an upcoming faulty graphics card? Or even something else like logic board or power supply? No ACPP