This error appears after Windows has failed to apply an update on your system. Sometimes this process just stops and hangs forever, in those situations this article can help you to get unstuck from “We couldn’t complete the update undoing changes don’t turn off your computer” but please remember that this can be a very nasty error to fix. [...]
You get this message when you attempt to load your user account after typing in your password.
“The User Profile Service Failed the Logon. User Profile Cannot Be Loaded”
Then Windows will restart due to the corrupted user account. (Infinite loop.)