lock computer instantly

There is a time when you want to walk away from your desk for a while and you don't want to turn off your computer and then nobody can peek your data in your pc. Windows XP provide you with the instantly "lock" feature. The following is what you need to do to instantly lock your computer so that a password is required when anyone wants to access it:
To lock your computer, simply press the Windows Key + L. For identifying Windows Key, you need to find the key, on top of which there is a "Flying Windows" logo. Any files or programs you have open will be hidden and you will need to enter your password to get in again.

You should note that this security measure will only be available if you have the computer configured to require a password when you log in.

If you cannot get it work, you need to check if one of the windows services called "Fast User Switching" was disabled. This feature needs the windows service, "Fast User Switching" to be enabled.