on screen before login, click the power button
before doing anything, hold down shift and click restart PC
this should load you into advanced startup
two choices
start up repair:
choose troubleshoot
choose advanced
choose start up repair - this will scan PC and maybe fix this - will ask for logon info
if that doesn't help, try Safe mode:
choose troubleshoot
choose advanced
choose start up options
hit the restart button
choose a safe mode (it doesn't matter which) by using number associated with it.
PC will restart and load safe mode
simply going into safe mode could fix it
I can't help you get password but we can try to help you login