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Mac wont start after Big Sur

My iMac wont start after upgrade to Big Sur


Posted on Jan 31, 2021 7:30 PM

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Question marked as Top-ranking reply

Posted on Feb 2, 2021 3:13 AM

Even if you’ve already done these basic resets do them again, two or three times each.

Reset the SMC How to reset the SMC of your Mac - Apple Support

Reset the NVRAM Reset NVRAM or PRAM on your Mac - Apple Support

After you boot into safe mode and shut down will ot boot again in safe mode?

5 replies

Feb 1, 2021 8:13 PM in response to SeaPapp

Thank you for your input. I tried this and several other online suggestions. Right now I have reinstalled Mohave. I tried a fresh update to Big Sur and everything went well until the very end where it says it has to shut down to complete the installation. It shuts down, won't complete install and becomes a brick. The only way I can get back in is Power/Command-R to disk utility. Now I running Mohave but can't turn off the computer at all. It won't restart. It wakes up fine from sleep mode.

Feb 19, 2021 7:51 PM in response to SeaPapp

Just a quick follow up and "Thank you". I went through the resets multiple times, but computer still wouldn't boot up (even in safe mode). Reinstalled Mohave and stayed with that until I could see a significant window of time. These failed upgrade attempts were leaving me stranded for hours. Tried the resets again. I also opted to install any Mohave patches or updates I could find. Not sure which one did the trick but when I hit the upgrade to Big Sur button, it worked! The process went smoothly, and the computer rebooted just like it should. Thank you again for following up and your suggestion.

Mac wont start after Big Sur

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