This thread show about How to get administrator password without old password(Knowing)
This is use only for education and not for other.
It doesnot require old password
Open Run command and type cmd in run command and hit enter.
Now cmd will be appear.
Type lusrmgr.msc in cmd window and then hit enter.
Now a new window is opened and click Users it shows the user names.
Select any user.In this is select the “venkatesh” user and the right click it.
It show the pop menu.
Select the set password..
Now click the proceed button.
Type the new password without using old password and then click ok button
Finally Click Ok button. Now you are change the old password
Thanks to http://www.vidyarthiplus.com
Thanks to V+