What did you do to him?
Personally, if i were you, i'd set a BIOS password, so he can't get on either. Set it so that you must enter a password to get past the BIOS (not only to get INTO the BIOS) and tell him if he'll take off the windows password, you'll take the BIOS one off. An eye for an eye 😈
Or else, just change the windows password. Google it, there's ways around it.