Much to my dismay, after upgrading my Mac to Sierra 10, I couldn’t connect to the internet, couldn’t use my secondary television display, and couldn’t access external servers. Panic time? Not at all.

The solution to get back up and running took less than five minutes. I rebooted my fresh install of Sierra into SAFE MODE by holding down the SHIFT key from just after the chime until the Mac icon displayed on the screen. After allowing the machine to fully boot, I shut it down Apple Icon > Shut Down) and performed a traditional restart. Then everything worked as expected.

Before you drive yourself crazy troubleshooting an upgrade-gone-wrong, try booting into SAFE MODE first.