Just picked it up yesterday, took it home and was in the middle of updating the OSX software. Left the room and came back in a 1/2 hours and it was shut down. Did the update again thinking maybe it was done and had shut it's self down normally but after 10 minutes into just downloading the update the fan started to roar and it simple turned it's self off, again. After that I gave up on downloading the update and just started playing with the OSX software when the fan kicked in and it turned off again. Back in the box for return today. I would get another to replace it but have lost my confidence and will just pay the 10% to get my money back. I still love my iMac!