Tutorial: Fixing an Unbootable Mac

Discussion in 'Apple Hardware' started by RHochstenbach, Aug 9, 2008.

  1. RHochstenbach

    RHochstenbach Administrator

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    Fixing an Unbootable Mac
    In this guide I'm showing a few steps that you can take, when your Mac doesn't boot. In most cases you see the boot screen, with a question mark.

    Note: To use hotkeys and the console, you need to use a USB keyboard and not an Apple wireless keyboard, as the bluetooth support gets loaded at a later stage in the boot process.

    Check if the problem is solved after each step. If not, then continue with the next step.

    1. Reset the PRAM
    Hold down ALT + CMD (Apple key) + P + R while turning on the Mac. This clears some settings that could cause driver problems.

    2. Safe boot
    Hold the SHIFT button while turning on the Mac. Hold it until you see the Apple logo. It wil now check the boot partition. When it's finished loading, you see the desktop, with the word 'Safe Boot'. Now restart the Mac.

    3. Single User Mode
    Hold down CMD + S while turning on the Mac until you see a black background with white text. enter the following command:
    fsck -fy
    It will now check the OS and file system. After this is done, enter the following command:
    4. Installation Disc
    Put the installation disc in the drive. To open the drive, hold down the mouse button (or both depending on the mouse used) while turning on the Mac. After you've inserted the disk, turn off the Mac and turn it back on while holding the C button. Choose the Utilities section, and choose to repair the disk.

    Still not working...
    In this case there's a larger problem that can't be fixed with utilities. In that case you need to reinstall Mac OS X. You can use the installation disc to do that.

    You can backup your data in 2 ways:

    1. Time Machine; In case you got a Time Capsule or a Time Machine backup, then you already got a backup. You can restore it after the installation.
    2. 2nd Mac; If you got a 2nd Mac, connect both Macs with a Firewire cable, and then turn on the failed Mac while holding down T (Target Disk Mode). Now you can copy the data to the 2nd Mac.

    If that doesn't solve it either, you got a hardware problem. In that case, go to an Apple Reseller.

    Good luck!
  2. Sniper

    Sniper Administrator Staff Member

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    fixing an unbootable Mac

    nice one, I might need to in the future but hopefully not :)
  3. Nicolai Sylvest

    Nicolai Sylvest Geek Trainee

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    Hi, I have a macbook pro model 2010-2011. I7 processors.

    I tried to update it to Yosemite. It made an error and went off. I tried to turn it on again. It loads the grey screen with the apple logo, and loads a boot bar. When it's done loading that after a couple of minutes, it just turns off automatically.
    I tried to back it up with an external drive with disk utility but it can't.
    I tried to run it in single user mode, but it cant check the os as it says that there is some wrong values in the volume I think. And it can't repair it. It just keeps looping from that point, till I manually turns the machine off.
    It cannot safe boot either.

    I do not have another mac or an installation disc.

    If I could just get it backed up so that I could re-install the osx.

    Hopefully someone can help.

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