I had my Macbook repaired and when it came back to me, it's running on Windows already. How do I revert back to my Mac OS?

  • 2
    Who repaired it ? Did you already have a dual boot ? Do you still have the installation DVD ? Apr 23 '13 at 14:37
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    Are you looking for an article explaining how to restore some backup format or an article on how to reinstall the OS on your Mac? Without further data, we could direct you to apple.com/support/manuals for steps needed to reinstall the OS or here.
    – bmike
    Apr 23 '13 at 14:38
  • Which version of Mac OS did you have? If Lion or Mountain Lion, try booting with command-R to see if there is a recovery partition you can use to re-install the OS over the internet.
    – GEdgar
    Apr 23 '13 at 14:55
  • You will need to provide more information if you expect a meaningful answer. What did you originally have the system repaired for? Was the repair shop Apple certified or an actual Apple store? What was your original operating system topology / configuration (i.e. were you running BootCamp). Do you have a backup to restore from?
    – Mort
    Apr 23 '13 at 14:59

Has MacOS been deleted or are you running in Bootcamp. Try restarting with the option (alt) key held down to see if you are presented with a choice of boot drives, and select the MacOS Drive.

Depending on which version of MacOS you had installed you may also be able to access the recovery drive

If MacOS has actually been deleted then take it back to the repairer and ask them to reinstall it...

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