A family member has recently bought an 21.5" iMac late 2010. I upgraded the OS from Mavericks to Yosemite via the app store. The computer was working fine for 8 days an now every time its booted it takes a few mins for the progression bar to fill and instantly boots in to the OS X Utilities. I click on Disk Utility and i try to repair/verify the main drive and i keep getting the same error message "The volume could not be verified completely. File system check exit code is 8. Updating boot support partitions for the volume as required. Error: Disk Utility can't repair this disk....e disk, and restore your backed-up files." We have no backup for the system as it was not needed and it was a clean install of the OS. I have tried to "Reinstall OS X' from the Disk Utility but the only drives it displays are Recovery HD (Locked) & EFI (locked and not correct format). So its missing a 500GB drive from the options. What can i do to fix this? UPDATE: I have tried to boot the computer while holding down the Alt/option key to select the bootable drive but i still only get the recovery.