A Master password is available in Windows XP,7,8 by default which decreases the probability of getting hacked into a PC which is known as "SYSKEY".To enable Syskey just  follow the steps below:-
It's Basically a SAM Lock Tool !
Well Once you have enabled it ! you can't disable it until your next Format !

Step 1. 

Start >> Run

Step 2. 

Type SYSKEY

Step 3. 

Enable Encryption

Step 4. 

Update (Restart)