I had a problem a few years ago getting into a Windows 2000 system. I found a free password cracker that did the job. It worked on everything up to Win XP - don’t know if it will work w/Vista or Win 7.
It is called Bootdisk and you create a boot disk [Linux-based]. Then, you shut down the computer, insert the disk, and turn on. Bootdisk then starts the computer in Linux and runs its program - follow the instructions and it will re-set the password to nothing [that is, if you get a password prompt the next time you boot up - hit Enter]. Then, you shut the computer down, remove the disk, and re-boot.
Windows will then start up. Then, you need to change your Admin rights ...
The URL is: at http://home.eunet.no/~pnordahl/ntpasswd/.
There are also other programs available - Google “bootdisk, crack, password, etc. ...
I am not computer savvy when it comes to booting, etc. I am very hesitant to try anything.