New 27" Mac, was going to reinstall El Capitan. Followed these instructions : https://support.apple.com/kb/PH21973?locale=en_US&viewlocale=en_US Now in Disk Utility the indented Macintosh HD drive is missing. When I go in to reinstall the OS X ,Macintosh HD is missing. I tried starting in about every mode with no success. With a tech at apple for an hour couldn't figure it out and said I needed to bring it in. Seems strange that there isn't anything I can do. I have an appointment at the apple store but I thought I'd see if anyone had advice so I could forego the appointment. Thanks in advance for any help!