My 27 inc iMac (bought in July 2011) is acting really strange. I've been away for one week, and the iMac has been disconnected from the power outlet during this time. When I first tried to power it on, nothing happened. Absolutely nothing. Imagine pressing the power button with the power cord disconnected. That's how it was. I tried plugging it out and back in, with or without USB devices etc, but it was just completely dead. All I could do at this point was to call Apple, so I disconnected everything and laid the iMac face down on the sofa in order to see the serial number. Then, when I plugged it back in, it started on the 4th or 5th attempt. Everything was working fine. Then, I powered it off and tried to start it again. Guess what? Dead again. After pressing the power button about 15 times, it started again, and now I'm too scared to turn it off. Restarting works. It was working 100% perfect before I left. There's nothing wrong with the power strip it's connected to. What the h*ll is going on?