My iMac was working fine until today I got the beachball of death and it took a long time, so I had to manually shut down my computer. Upon restarting it, I get a screen with a circle and a line going through it. I tried to restart my mac again using CMD+R to get into recovery mode, and went into Disk Util, and it showed my Macintosh HD as red, it ask to fix or ignore. So I click on fix thinking it would fix it, but instead it formats my entire drive. All 3TB of information gone. Sigh... I lost everything. And now I can't even reinstall Mac OS because it Disk Util keeps telling me it can't unmount my drive. I am trying to erase it. Does anyone know how to fix this? I've had such a terrible day because of this. I already did very permissions and repair in disk util and it shows everything as being okay. So I'm not sure why I can't even format my drive, it keeps saying unable to unmount. Prior to this my drive was unmounted so I'm not sure what the deal is. I heard some people telling me that I can force unmount it, but how can I do this when I don't have an operating system anymore? Please help anyone.