Hello, I have 27" (late 2012) iMac. Today I have tried to boot into Windows/bootcamp (in case to flash my smartphone). I did this normally 2-3x times per month for last one year with no problem. But today, for the first time, my iMac stuck on white boot screen. I hold Power button to turn off, wait a few seconds and turn in on again. Because I set (in OS X) to boot into Windows, iMac is now automatically booting into Windows. But the biggest problem is than iMac now can't recognize my wired keyboard (I bought new one 2 weeks ago). I tried to connect this keyboard to my MacBook Air (for check if is working) and yes, it's working, so there is no program with keyboard. The problem is than my iMac is not detecting keyboard in anyone of 4 USB ports on the back side. So I can't do anything, because iMac don't recognize the Option key holding while booting (for change to boot back to OS X). Do you have any idea where can be a problem and how I can fix it?