Few days ago i change my windows -7 Administrator Password and my friend again change it and gone away . I try Following method and got Password reset.
1. Start windows in DOS Mod
2. at DOS Prompt i came on root (C:>)
3. Check accounts by Typing c:> net user and Press Enter
4. User List
5. Again C:> net user Administrator Press Enter
6. Again Enter To Reset Password

Start again computer and Administrator has no Password :)
If there is another way please share with me.