To find Windows 7 password, there are some ways supported:
1. Ophcrack can easily find Windows 7 passwords if it is not strong enough and can be found in the dictionary:
http://ophcrack.sourceforge.net/
You can burn it to a CD or create a bootable flash drive and boot from either of the two.
2. If Ophcrack can't find the password, your next option is to simply erase the password since you don't know or have forgotten what it anyway. One software that comes to mind is pro Windows Password Recovery Tool which can do the trick on how to retrieve Windows 7 password: http://youtu.be/17IhUOGK1Tc