Error message: The macOS installation couldn't be completed

Out of the blue, I couldn't click or do any action on an internet page. The only thing that worked was the menu bar and favorites bar. I restarted my MacBook Air and after a minute or so go the error message: "The macOS installation couldn't be completed" along with some choices. I restarted my Mac and the same thing happened. I shut down my Mac and restarted and the same thing happened. Shut down and restarted again; same thing. What do I do? Note: the installer log shows in the background behind the error message.