My Mac has really been wrung through the wringer lately, and the story I’m about to tell is fairly anticlimactic given the preceding sequence of events. Nevertheless, let me summarize.
The story up until now:
A number of weeks ago, maybe four, maybe more, my iMac suddenly began powering itself off. Lots of troubleshooting was troubleshouted,1 and in the end, the Mac went off to Apple to receive a heart transplant in the form of a new system board.2 Some weird things happened and Apple had to go through more than one, but suffice it to say that now I finally have a new system board that both meets the original specifications and passes Apple’s diagnostics, something neither of two previous would-be replacement boards couldn’t manage.
The story now:
Then yesterday, I decided to fire up Safari and watch Netflix while I rode my bike indoors on the trainer, and instead of Anthony Bourdain and company, I was presented with a green rectangle and some blocky garbage at the top. Ditto for anything I tried to watch on Amazon Prime Video and Hulu.
Finding that the offending and therefore offensive videos played as expected in both Firefox and Chrome, I started digging around in Apple’s Discussions support area. I’ve found that for some reason Googling or DuckDuckGoing won’t always bring up the relevant threads from discussions.apple.com, which is too bad because I’ve found the answers to a lot of problems there. My lovely green video was not to be any exception.
Reinstall High Sierra. That’s the answer. Reinstall it.
You don’t need to nuke and pave, this isn’t difficult, destructive, or any other d-word. However you should back up beforehand, just like you should always back up for anything exciting like upgrades, updates, and the simple passage of time.
Restart your Mac and hold Command-R until you see an Apple logo. You’ll eventually find yourself booted into recovery mode, and the kindly offered utilities window includes an option to reinstall macOS.
Choose it and use it. Make sure to select the current boot drive, if you have more than one, so that High Sierra is reinstalled over top itself.
You may have a few reboots and possibly a couple extra password type in sessions, but that second point probably applies to people like me who have FileVault enabled on their hard drives.
After you’re done, you can fire up Safari and try out all the videos and rejoice. Have a nice nap — you’ve earned it, or close enough for government work.