Not sure what could be going on, but maybe try going through the steps
Type control userpasswords2 in the search box and hit enter
If the check box is checked where it says "Users must enter a user name and password to use this computer" uncheck it
Select your username and click apply
Type in your password twice OK and OK
Reboot
Then do it again only this time reverse the process by checking the box
Reboot again and see if that process sorts anything out.