this is a very useful and important TRICK that a HACKER must know. Many of the PC are password protected and sometimes it happens that you lose it's password. But from now even though if you forget the password of your windows account you will be able to open it as normal. I will show you how to log in on any computer without knowing the password.
Here we go,

WINDOWS XP LOG IN SCREEN SHOT.

§  Start the PC and wait till the log in screen appears .

§  Now press ctrl+alt+del together 3-5 times.

§  A windows XP classic log on screen will appear.

Windows XP classic log in screen

§  Now type User name : Administrator.

§  Leave Password block blank.

§  Now click on OK and you will be logged on to WINDOWS XP.

§  Now if you want you can Change OR Remove the password of your account through CONTROL PANEL>USER ACCOUNTS. 

this trick will only work if your os is windows xp it wont work in windows 7