Welcome to Apple Support Communities. I understand that you're unable to log in to either user account on your MacBook Pro, and when you try it won't move past the completed loading bar. I know how important it is to rely on using your Mac; I'd like to help. I'd suggest that you follow the steps here to start your Mac in safe mode: Use safe mode to isolate issues with your Mac
In safe mode, test to see if you can log in to either user; if so, restart normally and try again.
Let me know what you find.