Another trick for a stand alone windows 7 box is booting off a live linux USB, and do the following:
- pick an input utility to bugger with. In this case, the on screen keyboard
- rename that utility (osk.exe to osk.old)
- rename cmd.exe to osk.exe
- reboot into windows
Now you can call the osk from the login screen, which will in fact run cmd.exe with full admin rights.
Then resetting the password is a simple command: net user *username* *newpassword*