How to cracking the administrator user in Windows 7

First you should to boot with your CD. Click in Repair your computer. Press shift + F10. Then backup the  sethc.c, the PATH is c:\windows\system32\sethc.exe. Now you can replace the cmd.exe in the SYSTEM32:

copy c:\windows\system32\cmd.exe c:\windows\system32\sethc.exe

Reboot the system and press shift five times. This start a command prompt. So you can use the following commands for reset the administrator password:

net user Administrator *

Digit and confirm the password.

Source: http://www.wikihow.com/Hack-Windows