1. Open the command prompt (Start->Run->type cmd->Enter)
2. Now type net user and hit Enter
3. Now the system will show you a list of user accounts on the computer. Say for example you need to reset the password of the account by name John, then do as follows
4. Type net user John * and hit Enter. Now the system will ask you to enter the new password for the account. That’s it. Now you’ve successfully reset the password for John without knowing his old password.
I hope it helped atleast someone.:-)