There is no "Block Messenger" feature. I assume you mean "Lock Messenger", if so then you should see this icon in your system tray (the bottom-right corner of your screen).
Just double-click it.
EDIT: Ok I'm a bit slow
Attachment:MessengerLock_DefaultIcon.gif (636 bytes) This file has been downloaded 304 time(s). This post was edited on 01-23-2007 at 08:11 PM by Eljay.