If you have a kali linux live cd, it comes with a little tool called chntpw.
Just grab the SAM file (C:/Windows/System32/config/SAM), make a backup of it, and use chntpw in the terminal to clear the password (pretty easy to use understand). It wont help you if you need to know the password but will let you log into an account in a couple of minute, and you will then be able to change it.