NORMAL SHORTCUT KEY=WIN KEY+L
1. Right-click on your desktop (on any blank area) and select New > Shortcut.
2. Type rundll32.exe user32.dll,LockWorkStation in the “Type the location of the item” filed in the window and click next.
3. Give a name to the shortcut (something like Lockdown My PC) and click “Finish” to complete the setup.
4. Now the shortcut for locking down your computer appears on desktop. You can even customize it by adding some colourful icon to it.
Clicking on it will lockdown the computer. This works well on Windows XP, Windows Vista and even on Windows 7. You need to login back to your computer by providing your credentials if you need to unlock it again.