okay so I downloaded 10.9 and installed it. I can no longer boot up into my main HD. just spools at the apple logo for hours. I went into recovery and repaired the permissions and the disk. both had errors when I vrified them. still couldnt boot up. so now I want to see how to go back to mountain lion. I cant downgrade from recovery because it wont allow it because im already in a newer version. if anybody could help me it would be much appreciated!