It seems when you uninstall Messenger (using the tweaks on this site) the policy is automatically set to prevent it running.
This causes the symptom of clicking on the Messenger shortcut and seeing an hourglass for a second or two but the program not loading.
To get Messenger installed again requires more than just reinstalling the program from Windows Update or a downloaded installer.
After that you have to change the following registry entry with regedit:
You should change the PreventRun value from (1) to (0)