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Today I found my Mac shut down. It won't boot again anymore. When I try to turn it on, it just shows the Apple logo, a loading bar and after 1/3 progress it just shuts down again.

After some research I learned how to access the Disk Utility by pressing Command ⌘-R at boot time. Apparently the problem is with the hard disk, since when I try to repair it it says that it can't be repaired and needs to be formatted.

I have an external disk where I backed up the whole system using Time Machine. I'm just not sure how to proceed now.

After accessing the Disk Utility I have 4 options, the first of which is restoring a Time Machine backup. The thing is that if I try this one it lets me restore a backup only in the other partition of the external HD, and not on the disk on my Mac. Why is that? What shall I do?

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3 Answers 3

Reset to default
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Since it says you need to reformat, what you need to do is:

  1. Boot into the Recovery Partition
  2. Click "Disk Utility"
  3. Select "Macintosh HD"
  4. Go to the "Erase" tab
  5. Select the format as "Mac OS Extended (Journaled)"
  6. Choose a security option from the security option section(I would recommend zero-pass since this is still your Mac) NOTE: If you have an SSD, the security options button will be disabled. This is normal
  7. Hit "Erase"
  8. It may take a while or be stuck. Don't worry. Give it time. The progress bars and estimated time on OS X suck
  9. After it is done, close Disk Utility and go to "Reinstall OS X"
  10. Select Macintosh HD and then proceed as if you were setting up a new iMac without your old backup
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  • it's the first time I format or reinstall a Mac. After these steps will I be able to recover the backup from time machine?
    – Carlo
    Commented Aug 21, 2015 at 0:14
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    Yeah. Don't worry, I would be surprised if you had zero questions. After you erase the disk and reinstall OS X, it will lead you through a step by step procedure to set up your mac. eventually, it will give you the option to restore from Time Machine. Click that, plug in the backup drive, then follow the onscreen instructions. It should probably be a better idea to have the backup disk unplugged until this step.
    – SentientBacon
    Commented Aug 21, 2015 at 0:19
  • Followed up till step 7. Error: "Erase process has failed"
    – ChristoKiwi
    Commented Jun 20, 2020 at 6:36
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Go to "Window" --> "Log Window" and try to find some errors. For me helped reformat my drive to GUID (GPT) partition table in Disk Utility.

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  • +1 to this answer - I got my SSD serviced by the manufacturer and the Time Machine System Restore tool wouldn’t restore onto my erased SSD until I reformatted it with a GUID partition table in Disk Utility. Once I did this, the restore proceeded with no issues. And no need to fresh install MacOS..
    – Dylan Kirkby
    Commented Mar 29, 2021 at 19:28
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What you need to do is reset your whole system. Note that if you did not back up applications or such, these will be gone.

Boot into the Recovery Partition, and erase your hard disk. You can do this by going to the Disk Utility and selecting your hard disk. (Your Mac's hard disk, NOT your Time Machine backup of course.) There are a couple of tabs at the top, you need to select 'Erase' and there will be a button with the same label that you will need to click. This might take some time.

After doing this, go back to the main screen of your Recovery Partition and select 'Reinstall OS X'. This might install the newest version of OS X. Installing OS X might take up to 1 hour.

After having reinstalled OS X, boot your Mac. You will now be able to transfer your data with the Migration Assistant within the Setup Assistant. After doing this, continue with the installation as you normally would, and after finishing, try to see if your installation is identical to your previous one.

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