Make sure that you do the following on your computer or another computer with the owners permission only.
If you don't want to change the password:
1 > Get a program called Ophcrack(very large. 496Mb)
2 >> Download the liveCD (ISO)
3 >> Burn the ISO to a CD using an ISO burner
4 >> The Live CD's come with the free rainbow tables, so you might need to download other tables (cost money)
4 >> Bootup from the CD
5 >> Crack the SAM and System file
Another way is to remove Windows password.
You should try freeware: Offline NT Password & Registry Editor
or shareware: Windows Password Reset Standard!
Offline NT Password & Registry Editor is not easy for new user!
Windows Password Reset Standard is too easy to use, then you can login back in 5 minutes!