While using Windows 7 (via Bootcamp) I shutdown my 27 inch 2011 iMac. After it was shutdown I pressed the power button to turn it back on, it proceeded to play the startup sound and then froze on a white screen. There is no cursor or anything else on the screen. I tried unplugging all cables, including the power, reconnecting only the power and attempting to turn it back on with the same result. It does not respond to any key combinations. Holding Alt while it boots does not bring up the disk selector. Holding T does not put it into Target Disk mode. Holding Cmd-Opt-R-P does not have any affect. Holding Shift does not put it into safe mode. Holding Cmd-V does not bring up verbose boot. I made a copy of the OS X Recovery Disk onto a USB but am unable to use it as the Mac won't boot from it (and won't bring up disk selector to select it). It was working fine minutes before I shut it down and then suddenly refuses to boot and I am at a loss as to what to do (and there are no Apple Stores or "Genius Bars" in this country).