|Ah. Well Try booting into Safemode with Command prompt.|
See if a black box appears. If so, you can enter this
net user username *
Replace username with the user with the password. I think that makes sense.
So If the user is Betty, you would put
net user betty *
Hopefully that will forcefully change the password, With my XP laptop it works, I have no idea whether it will for you.
If it doesn't, You either have to reboot it to factory settings, or use cracking software to break into it.
Or you could take it into a Tech shop and they might be able to do it for you. But could cost.