After Setting a shortcut to unlock messenger for example CTRL+L nothing happen after pressing the keys to unlock messenger and the only way to open messenger is to kill the process it task manager and start messenger again !
Live messenger version is 2009 build 14.0.0.8089
Messenger live version is 4.83.0.372
pressing the lock button does not work if you want to unlock it in 7. To unlock messenger without having to end the messenger process you can double click the magnification glass like Krissy-afc said. If the icon does not show in the bar or the popup then restart messenger.