Hoping someone can help me because Apple were unable to do so over the phone and don't seem to offer Genius Bar assistance for iMacs. I'm trying to factory restore my iMac 5K late 2014 model as I'm selling it. I've gone into the CMD R screen, deleted the partition I was advised to in the written instructions. Click on install new OS X, go through and agree to everything for El Capitan. Then it asks which disk is this being installed too... Only a Back up HD shows, which is locked and not an option. Over the phone I was guided into the Internet recovery, told to check out the Macintosh HD and hit repair. Went through all good and green. Went to Reinstall OS X. Go to install YOSEMITE as it's the default OS X. I'm again asked to select a disc in which there is nothing to select. I was then guided into the terminal screen but the command code for discutil were not showing. I've googled the hell out of this and it all seems to be people adding new Hard Drives... The resolutions dont seem to apply. The only discs that show are Macintosh HD, below this is a line which follows with disk2 and OS X Base System coming from it. If someone could please assist it would be mostly appreciated.