My MacBook Air won’t shut down on its own.

How to fix an Apple Mac that won't shut down

There's no simple answer to fix a Mac that has problems shutting down. It could be caused by a variety of different problems. Here are some troubleshooting steps that we advise you to try. Go through each one at a time and see if it solves the problem:

• Try to determine if one particular app is causing the problem. If one app always freezes when you shut down and cancels the shutdown process then update it (or re-install it).
• Perform a software update (open App Store and click Updates > Update All).
• Update any software that you installed outside of the App Store. Typically open the App and choose Help > Update or App > Update Software.
• Check that you have FileVault turned off (System Preferences > Security & Privacy > FileVault > Turn Off FileVault).
• Open Disk Utility. Choose the main hard drive and click Verify Disk. If there are any problems click Repair Disk.
• Choose the main volume in Disk Utility (underneath your main drive) and choose Verify Disk Permissions > Repair Disk Permissions.
• Reset the SMC. Follow this Apple Support article.
• Backup and reinstall Mac OS X.

This may help with your performance issues as well as most other issues:

A Troubleshooting Procedure that may Fix Problems with macOS El Capitan or Later

You should try each, one at a time, then test to see if the problem is fixed before going on to the next.

Be sure to backup your files before proceeding if possible.

1. Shutdown the computer, wait 30 seconds, restart the computer.
2. Disconnect all third-party peripherals.
3. Resetting your Mac’s PRAM and NVRAM
4. Reset the System Management Controller (SMC)
5. Reset your Startup Disk and Sound preferences.
6. Start the computer in Safe Mode. Test in safe mode to see if the problem persists, then restart normally. Also, see Use safe mode to isolate issues with your Mac - Apple Support and Playing Safe- what does Safe mode do?.
7. Use Apple Hardware Test to see if there is any hardware malfunction. How to invoke and interpret the Apple hardware tests - CNET.
8. Repair the disk by booting from the Recovery HD. Immediately after the chime hold down the Command and R keys until the Utility Menu appears. Choose Disk Utility and click on the Continue button. Select the indented (usually, Macintosh HD) volume entry from the side list. Click on the First Aid button in the toolbar. Wait for the Done button to appear. Quit Disk Utility and return to the Utility Menu. Restart the computer from the Apple Menu.
9. Repair permissions on the Home folder: Resolve issues caused by changing the permissions of items in your home folder.
10. Create a New User Account Open Users & Groups preferences. Click on the lock icon and enter your Admin password when prompted. On the left under Current User click on the Add [+] button under Login Options. Setup a new Admin user account. Upon completion log out of your current account then log into the new account. If your problems cease, then consider switching to the new account and transferring your files to it - Transferring files from one User Account to another.
11. Download and install the OS X El Capitan 10.11.6 Combo Update or 10.12.6 Combo Update or Download macOS High Sierra 10.13.5 Combo Update as needed.
12. Reinstall OS X by booting from the Recovery HD using the Command and R keys. When the Utility Menu appears select Reinstall OS X then click on the Continue button.
13. Erase and Install OS X Restart the computer. Immediately after the chime hold down the Command and R keys until the Apple logo appears. When the Utility Menu appears:

1. Select Disk Utility from the Utility Menu and click on Continue button.
2. When Disk Utility loads select the drive (out-dented entry) from the Device list.
3. Click on the Erase icon in Disk Utility's toolbar. A panel will drop down.
4. Set the Format type to APFS (for SSDs only) or Mac OS Extended (Journaled.)
5. Click on the Apply button, then wait for the Done button to activate and click on it.
6. Quit Disk Utility and return to the Utility Menu.
7. Select Reinstall OS X and click on the Continue button.

14. If none of the above helps then see How to Downgrade macOS High Sierra and macOS Reversion- How to Downgrade from High Sierra.

15. If you get here without success then make an appointment at the Apple Genius Bar for service. If you need to find an Apple Store - Find a Store - Apple.