Well, that is very informative – but indeed it is, which tells us to look into the registry. So I boot into the command prompt, go to D:\Windows\System32\config which is where the registry is stored. In this directory there is a hidden folder called RegBack which is a backup of the registry. That is our savior.
So I created another backup folder, copied everything into the backup folder, and used the files in RegBack to overwrite those in D:\Windows\System32\config. Reboot, and the system is back to life.