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iMac keeps restarting without booting up

My iMac suddenly shut down (had a flicker of a blue screen right before) and restarted, but did not get all the way booted up, and then restarted again. It keeps doing that until I manually shut it off. Checked the power supply and did the whole "wait for 30 seconds and then start again" routine multiple times. But its the same behavior. Tried pressing Shift-S and then Apple+S to start in safe mode - did not work. Neither did Shift-R or Apple-R for recovery mode. The device is about 8-9 years old.

iMac Line (2012 and Later)

Posted on Oct 19, 2020 10:49 AM

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9 replies

Oct 19, 2020 7:11 PM in response to BDAqua

Thank you for your response!! I had tried the Shift key before and it didn't do anything. Tried it again, but nothing changed. Holding the Option key down did give me a choice of which mount to use - the standard disc or the Recovery disc. I chose "Recovery" and it started to boot, BUT it stopped at a grey screen and is now stuck there. Tried again and chose my standard disc, and the same thing happened. I can also choose a WiFi network to join, but that didn't make a difference either. Next - I'll see if I can connect my Macbook to this iMac and try to boot it from there. Someone asked me to try that. Any experience with that method?

Nov 2, 2020 2:44 PM in response to BDAqua

I connected my Macbook to the iMac using a Thunderbolt cable, booted the Macbook with "t" pressed, and then started the iMac with "alt/option" pressed. The Macbook's disc is not showing up as a boot-up option. However, when I restarted the iMac while holding down the "t" key and the Macbook while pressing "alt/option", the iMac's hard drive showed up in the Macbook. I didn't boot from there because the iMac is where the problem is and not the Macbook, However, I was at able to take a data backup onto an external drive. So that was good.


But I'm still not able to boot the iMac from the Macbook.

Nov 11, 2020 7:28 AM in response to BDAqua

BDAqua - first of all - thank you for your responses. They seem to help me get closer to the elusive goal. I was able to successfully mount the iMac drive on my Macbook through the Disc Utility and run a first aid repair. It ran successfully - but when I tried rebooting the iMac it still had the same behavior - booting up to a grey screen and then automatically rebooting again and again. Macbook OS is Mojave 10.14.6. I don't remember what the iMac was on, but it was most likely the most updated version as of early 2020.

iMac keeps restarting without booting up

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