To restart Windows Live Messenger completely without rebooting:
-Hold the WindowsKey and press R, a little window titled "Run" should open.
-Enter "taskmgr" and press Enter.
-In Windows Task Manager, go to "Processes" and find "msnmsgr.exe"
-Right click that process and select "End Process."
-Close the Task Manager
Wait about 5 seconds and start Windows Live Messenger again from your Program list. This time around though, make sure you know the code before you lock it.