How to open a password protected locked PC in windows without knowing the password

Method 1 : First Turn on the computer,

Wait until windows asks you for your password,

When prompted for a password, type: ctrl+Alt+del

A new screen pops up

In the Username Field type: Administrator

Leave the password field blank.

Press enter

And you are in.

This only works if you have admin account with no password.   

Method 2: boot in safe mode press F8 while booting.

go to user accounts and remove password 

Method 3: On windows XP, you can try this:

Boot the computer and press Ctrl + Alt + Delete two times when you See Windows welcome screen / login screen. It'll show classic login box. Now type "Administrator" (without quotes) in username field and leave password field blank, press Enter and you should be able to login Windows.

Now you can reset your account password from "Control Panel -> User Accounts".

If that doesn't or you use windows 7 or vista, try this:

• Enter a computer that can link to Internet. Download windows password recovery Tool 3.0 and install the software on that computer.
• Run the software and create windows password reset disk by follow the instructions.
• Eject the created CD/DVD and insert it into the locked computer.
• Reboot the locked computer (it's necessary for you to change your locked computer's BIOS setting to make it boot from CD drive) and then follow the instructions to reset your password.
• Now login Windows and set a new password