Mac Won't Boot or Start After macOS Big Sur/Catalina/Sierra Update

This page addresses five solutions for the issue of a Mac not booting or starting after updating to macOS Big Sur, Catalina, Sierra, or an older macOS version. If you're experiencing this problem, follow these steps to get your Mac working now:

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macOS has now been updated to version 11.0, and numerous Mac users are endeavoring to upgrade to the latest edition. While for the majority, it's a seamless and enjoyable process, for some, this update has brought about unintended consequences. Users have reported issues where their Mac computers refuse to boot after installing the new macOS Big Sur or Catalina. When a Mac encounters problems, it typically manifests in the inability to boot or start up correctly. If you find yourself in this predicament, the top priority should be retrieving data from the unbootable Mac, because:

• Attempting to fix the Mac boot issue may write new data to this Mac, potentially overwriting old data and making it irretrievable.
• Recovering data beforehand can prevent data loss before attempting more complex fixes.

Tools like Mac Data Recovery Software can help retrieve data from unbootable Macs after an update. It creates a bootable media that allows you to recover data from your Mac's hard drive (if you have only one Mac). Additionally, it can recover data from failed internal Mac hard drives, APFS boot drives, and unmountable APFS boot volumes, etc. If you have two Mac devices, remove the hard drive from the affected one and connect it to the other Mac. Download Data Recovery Wizard for Mac on that second device and use it to recover data from the hard drive.

Step 1. Search for missing files

Choose the disk location to search for lost files (this can be an internal HDD/SSD or an external hard drive) where you experienced data and file loss. Click the "Search for lost files" button.

Note: Before proceeding with data recovery, it's recommended to click "Disk Backup" from the left sidebar to create a backup of your HDD/SSD to prevent any potential further data loss. Once the backup is done, the software can retrieve data from the backup, and you can continue using your HDD or SSD safely.

Step 2. Review the scanning results

This software will instantly scan your chosen disk volume and display images, documents, audio files, videos, and emails on the left panel.

Step 3. Select the file(s) and recover

Click on the data to preview it, and then click the "Recover" button to restore them.

Next, you can proceed to fix the "Mac won't boot after update" issue once you've successfully retrieved your data from the drive.

1. Reset the PRAM/NVRAM

NVRAM stands for Non-Volatile Random-Access Memory, which refers to specific memory areas on your Mac that retain data even when the device is turned off, such as volume settings and screen resolution. Resetting this data is harmless! Sometimes, following this procedure, your Mac will restart normally.

• Restart your Mac
• Hold down all of these keys: "Command", "Option", "P" and "R", and turn on the Mac. (This is the same key combination to reset the PRAM). 
• Continue holding the keys down until you hear the Mac restart again.

You might see a progress bar during startup. If the progress bar fills up and the Mac starts up normally, then you're likely all set. If not, proceed to reset the SMC.

2. Reset the SMC (System Management Controller)

In certain situations, you might need to reset your Mac's SMC (System Management Controller).

1. Shut down the Mac.
2. Unplug all cables.
3. Wait for a few minutes.
4. Reconnect the cables and start up the Mac.

If you have a Mac desktop, unplug it for 15 seconds, and then plug it back in. After five seconds, press the power button.

3. Boot Mac in Safe Mode

Safe Mode is a simplified version of the Mac operating system that can be beneficial when troubleshooting problems with your Mac.

1. Start your Mac, and while it's booting up, press and hold the "Shift" key. Ensure that your Mac has at least 9 GB of free storage available. 2. When the login window appears, release the "Shift" key and proceed to log in. If you have FileVault enabled, you might need to log in twice. After logging in, restart your device.

耐心等待Mac电脑完成重启过程。

4. Launch Disk Utility in Recovery Mode

If your Mac is booting but the operating system isn't loading, you might have a corrupted drive. Fortunately, you can address this issue in Recovery Mode. In Recovery Mode, you can restore from a Time Machine backup, use Disk Utility to verify and repair connected drives, check your internet connection, seek assistance online with Safari, and install or reinstall macOS.

1. Ensure that the Mac is turned off. If it's stuck on a grey, blue, or white screen, press and hold the Mac's power button for several seconds until it powers off. 2. Hold down the "Command" and "R" keys, and then turn the Mac back on. Continue pressing "Cmd" + "R" while the Mac is starting up. 3. Once your Mac boots into Recovery Mode, you will have access to "Utilities." Click on "Disk Utility," find the icon representing your Mac's drive, and click "Verify Disk."

5. Reinstall macOS Big Sur/Catalina/Sierra

The last method to fix the macOS Big Sur, Catalina, or Sierra fails to boot after update error is to reinstall macOS.

- You can download the desired macOS Big Sur/Catalina/Sierra and create a bootable USB drive to perform a clean installation of macOS Big Sur/Catalina/Sierra on your computer. - Alternatively, you can boot into Recovery mode (Solution 4), and then select to install the latest operating system, following the on-screen instructions. For more details on reinstalling macOS, refer to our article on resetting a Mac to its factory settings.

If your Mac remains unresponsive after attempting these suggestions, contact Apple Support or an authorized Apple Repair Center. It's probable that there is an issue with your logic board or other internal hardware.