In earlier post, I have described you how you can Reset your window administrator Password using "Offline NT Password & Registry Editor". Now I am Describing you another technique which doesn't required any tool and by using this technique You can change the Window Administrator Password without knowing it. Here are the simple step which should follow ...
1) log in  from Guest Account.

2) Go to C:/windows/system32

3) Copy cmd.exe and paste it on desktop

4) rename cmd.exe to sethc.exe

5) Copy the new sethc.exe to system 32,when window asks for overwriting the file,then click yes.

                          

6) Now Log out from your guest account and at the user select window,press shift key 5 times.

7) Instead of Sticky Key confirmation dialog,command prompt with full Administrator privileges will open.

               

8) Now type " NET USER ADMINISTRATOR asd” where "asd” can be any password you like and press enter.

9) You will see " The Command completed successfully” and then exit the command prompt and login into administrator with your new Password. Now you have hacked Admin from guest account.

Concept

Press shift key 5 times and the sticky key dialog shows up.This works even at the logon screen. But If we replace the sethc.exe which is responsible for the sticky key dialog,with cmd.exe, and then call sethc.exe by pressing shift key 5 times at logon screen,we will get a command prompt with administrator privilages because no user has logged on. From there we can hack the administrator password,even from a guest account.