About 2 months ago i had a problem with my video card. Brought it to the apple store and had the video card replaced. It is out of warranty. iMac worked great for about 1 month and then it started to power off by itself at random times. Brought it back to the apple store and they told me they found a problem with 1 of the fans and a loose bluetooth connection. They fixed those for free. It is now about another month since it was in and now the monitor will go to sleep at random times. I can feel air coming from the bottom vents and the mouse still lights up showing that the computer is still on. I can not get the computer to start back up by tapping the mouse or keyboard. Sometimes the computer monitor will turn back on when I hold the power button down for a couple of seconds. Other times it will not turn back on and holding down the power button turns the computer off. I have turned off the monitor going to sleep as well as the hard disk. the problem still occurs. Seems to be happening more frequently in the past 2 days. Any thoughts on the problem? Thanks.