Try logging in on safe mode.
Turn on the PC. Once you get to the login screen on the bottom right should be the Power Icon to shutdown, restart ect.
HOLD Shift then press the button and select restart and hold shit the whole time!
Then you should get a menu. Click on Trouble Shoot. Then on the next page should be windows start up i think? Right collum bottom option. Then tell it to restart. It will restart in safe mode and try logging in. If you can log in try just doing a normal reboot and see if you can get back in.
If you still can't get back in, go back to safe mode and we can turn off stuff to find out what the issue is.
Once in safe mode and logged in go to the start screen and then click the search button. Type in...