If you lost some important data after fixing Mac won't start after Sierra update, you must try professional data recovery software – Remo Recover data recovery tool for Mac to restore all lost data back. How to recover lost data due to macOS Sierra failure? For a faster reinstall, create a new bootable drive to clean install macOS Sierra on your MacBook again. To reinstall, restart your Mac and press Command + R at startup, then select Reinstall macOS option. If nothing seems to work, then you need to reinstall macOS Sierra. Here Disk Utility automatically run fsck to fix macOS Sierra fail to boot error problem. Press Disk Utility -> click on First Aid option and try fixing your Mac drive.

Launch Mac and press Command + R as it starts up.

Restart your system and wait patiently till it complete the reboot process. Steps to do this, turn on Mac and click Shift key when you hear the startup sound, then release it when you see the Apple logo.

Try to start your Mac using Safe Mode.

Wait for few seconds and press Power button to turn on your Mac.

Click and hold the Power icon for a few seconds until your Mac turns off.

Please try each of the solution explained here until your problem is solved:

Now let’s see how to fix MacBook / Mac won't boot after update Sierra is installedīefore continuing through any troubleshooting tips mentioned below, the first thing to do is backup up all your data from your Mac hard drive to ensure that it’s safe.

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