You can undo the unwanted changes from the Advanced Startup Options boot menu as follows:
- Press F8 while starting the computer to display the Advanced Startup Options menu.
- Choose Last Known Good Configuration.
Windows will start using a copy of the registry that was saved the last time the system successfully booted past the logon screen.
This is the perfect remedy for changes that render Windows unable to boot far enough for a user to logon.
Note that booting into this mode does not revert other files in the filesystem to their previous states. If file damage is preventing Windows from starting it is more appropriate to run System Restore from Startup Repair mode.