Last night I bought Mountain Lion and moved the installer to an 8GB USB stick in order to create a bootable drive to clean install it. I shut down my iMac, booted it back up again holding the option key, and two options came up. One was my main hard drive, and the other was the USB drive I had Mountain Lion installed onto. As normal I clicked the USB drive, and instead of another window popping up allowing me to access the Disk Utility, the white Apple screen with the logo in the centre appeared, and underneath the loading icon just kept endlessly spinning round. After about 2 minutes, the Apple logo changes to a circle with a cross through it, and the loading icon just continues spinning. I eventually had to just shut down my iMac via the button at the back. After that, I tried to format it again, and this time the same thing happened, but after the icon had span round a little bit, the screen went black and loads of white words popped up, followed by my iMac rebooting. Everything works fine still, but I just tried formatting again for the 3rd time, and the same thing I mentioned at the start happened - just endless spinning of the loading icon. I was wondering if this is a common problem or not, and is it easily fixable? Any help is appreciated, thanks.