Hi kg14,
Is the full error you're getting something like "The user profile service failed, could not connect to service"? And then it refuses to let you log in? As you mentioned it's booting you back to the login screen.
Just wondering as it happened to me randomly a couple of weeks ago. It was actually an Avast update that caused the issue, or possibly one of the latest garbage updates that's been pushed out from MS lately which caused some compatibility problems after I updated.
It's the first time it's ever happened to me, and wouldn't let me in to my account at all, I could only get in to the Admin account.
The only solution for me was to boot into WinRE (F8 on boot) and do a system restore, then uninstall Avast and reinstall an older version. Not sure if that's the specific error you're getting or you have Avast installed?