My late 2007 iMac, running Mavericks, locked up on me this morning and I had to do a hard restart. When it restarted, it gave me the screen that said I could either reinstall OS X, reinstall from a Time Machine backup or used Disk Utility to repair the disk. I tried to repair the disk but it failed, saying I need to backup my files and reinstall the OS. When I went to backup from Time Machine, it couldn't find the disk to backup to. So, is my HD done for?