If your MacBook Pro has started behaving abnormally or isn’t booting at all even after you’ve upgraded the operating system to the latest version (macOS High Sierra at the time of this writing), and have installed all the updates, it’s probably your hard disk that is causing the trouble and needs to be repaired.
- ■Get to Recovery Mode
Power on your MacBook Pro, press the Command + R keys simultaneously as the first screen appears, and release the keys when you see the Apple logo. This boots your MacBook Pro in Recovery Mode. From here you can restore your data from a Time Machine backup, re-install the operating system, manage hard disk partitions, etc.
Note: If your MacBook Pro is already on, you can click the Apple logo from the top-left corner, click Restart, click Restart again in the box, and press the Command + R keys as soon as the computer starts up again after shutting down to get to Recovery Mode.
■Get to Disk Utility
Select your language on the Language window, click the Next button from the bottom, select Disk Utility on the macOS Utilities window, and click Continue. This opens the Disk Utility window. From here you can manage all the tasks related to your hard disk(s) such as troubleshooting, managing disk partitions, etc.
■Unmount the disk
Select the problematic disk (Main for this example) from the left pane, and click Unmount. This unmounts the disk. Unmounting ensures that the disk is not in use during the repair process, and that the task is conducted without any unwanted obstructions or prompts.
■Repair the disk
Click First Aid, and click Run in the box that pops up next. This diagnoses the disk for any errors or inconsistencies, and automatically repairs them. Since the disk was unmounted, the repair should go smoothly.
■Check details (Optional)
Click Show Details once the repairing is done (or during the process). This expands the box and displays all the details that was collected during the repair process. This information may come in handy if there are some issues with the disk that First Aid couldn’t repair, and you want to look for other solutions rather than relying on the built-in tool.
■Re-mount the disk
Click Done on the repair disk completion box, and click Mount while the disk you just formatted is still selected. This mounts the disk back. After re-mounting, your MacBook Pro is all set to boot up normally.
■Restart your MacBook Pro
Click the Apple logo from the top-left corner, and click Restart. This reboots your MacBook Pro to the login screen. Here you can enter your account’s password and continue using the computer as before.