Restore From Time Machine Backup: Restore your Mac from an external hard drive or Time Capsule that contains a Time Machine backup of your Mac. Reinstall macOS (or Reinstall OS X): Download and reinstall the Mac operating system.

Feb 25, 2016 After entering Internet Recovery Mode and choosing to install or reinstall macOS, your Mac will need to download the installer for the version of macOS that came preloaded on your Mac when you took it out of the box.

How to reinstall Mac OS X: How to access OS X Recovery mode You access recovery mode by holding down the Command (Cmd, also known as the Apple key) and R keys during startup. Follow these steps to boot into OS X Recovery: