canius1
Level 1 (4 points)
Desktops

Q: 2011 iMac 27" using Sierra keeps rebooting

I installed Sierra 1-2 weeks ago.This morning, I tried to use my iMac and the screen flickerd for a couple of minutes, then  shut down and turned back "on" on its own.  Once the Apple icon with white background came up, the progress bar appeared. The bar got to the end of the end and then it shut down again.  I let the iMac go  through this repeated shut down  , turn back on , apple icon, progress bar , three times before I unplugged it. I waited 1-2 hours and plugged the it back in.  The same thing occurred. It appears to be in a shut down, start up loop.

 

Does anyone have an ideas?   I love this computer its 5.5 years old and I do not want to have to replace it

Posted on Oct 15, 2016 3:39 PM

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canius1

Q: 2011 iMac 27" using Sierra keeps rebooting

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  • by sarah_s1,

    sarah_s1 sarah_s1 Oct 16, 2016 5:59 PM in response to canius1
    Community Specialists
    Oct 16, 2016 5:59 PM in response to canius1
    Good evening canius1,

    I understand your iMac will not finish booting up this morning.  Has the computer restarted properly since you upgraded to macOS Sierra a couple of weeks ago?  Do you have a Time Machine backup of your computer?

    The first thing I would suggest is to boot your computer in safe mode.

    Try safe mode if your Mac doesn‘t finish starting up
     

    What is safe mode?

    Safe mode (sometimes called safe boot) is a way to start up your Mac so that it performs certain checks, and prevents some software from automatically loading or opening. Starting your Mac in safe mode does the following:

    • Verifies your startup disk, and attempts to repair directory issues if needed
    • Loads only required kernel extensions
    • Prevents Startup Items and Login Items from opening automatically
    • Disables user-installed fonts 
    • Deletes font caches, Kernel cache and other system cache files

    Together, these changes can help resolve or isolate issues related to your startup disk. 

    Starting up in safe mode

    Follow these steps to start up into safe mode.

    1. Start or restart your Mac. 
    2. Immediately after you hear the startup sound, press and hold the Shift key.
    3. Release the Shift key when you see the Apple logo appear on the screen.

    After the Apple logo appears, it might take longer than usual to reach the login screen or your desktop. This is because your Mac performs a directory check of your startup disk as part of safe mode.

    To leave safe mode, restart your computer without pressing any keys during startup.

    If you don't hear a startup chime after pressing the power key, see what to do if your Mac won't turn on.

    If your Mac restarts or shuts down in safe mode

    If your Mac automatically restarts in safe mode, OS X might have found an issue that it's trying to fix. 

    Safe mode performs a directory check of your startup disk, similar to what happens when you choose to verify or repair a disk using Disk Utility. If OS X finds an issue, the directory on your startup disk is repaired and your Mac restarts. 

    If your Mac turns itself off when you start up in safe mode, check the power connection on your Mac to make sure it's plugged in securely at both your Mac and the power outlet. If you're using a MagSafe power adapter, make sure the LED on your power adapter is yellow or green. Then, try starting up in safe mode again.

    If your Mac repeatedly restarts or shuts down during safe mode, contact Apple Support, or consult with an Apple Authorized Service Provider or Apple Genius for more help.


    Take care.