You can eliminate the possibility of any problem being caused by errors in your system by
  1. shutting down your computer,
  2. waiting 15 or 20 seconds
  3. rebooting while holding Option+Command+R
  4. run the installer from the Recovery Drive. Note: you may have to manually log onto your WiFi network as everything, including the Recovery drive is downloaded from the internet.


Option+Command+R installs the latest version of MacOS that is compatible with your computer as opposed to Command+R which installs the version currently installed on your computer and Shift+Option+Command+R which installs the version of MacOS that came on your computer from the factory or the closest available version.

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein