Guy coming in 5 hrs to buy my macbook, I told him I'd format it before he came. I tried formatting the hard drive but it said unable to unmount disk, so I tried downloading OSX from the app store AND IT SAYS I DONT OWN IT, I AM 100% SURE THAT I BOUGHT OSX MOUNTAIN LION!!!!! Help !!! I cant create a bootable OSX USB drive, and I cant format the HDD, what now??