Messenger has moved to Skype

Messenger was retired in April 2013 and is no longer available or supported on most Mac and Windows operating systems. *

You can continue to make audio and video calls with your contacts on Skype and Facebook and send IMs for free—your contacts will come with you when you update to Skype and sign in with your Microsoft account.
http://windows.microsoft.com/en-us/m...enger-to-skype