Hello Jorge, you joined just before I did
The first thing I would do is try a System Restore point from before the problem started if you have one. It is also often suggested to update to the latest version if you have not already. Uninstalling, then reinstalling is also a suggestion.
Here is something else to try. Try deleting the wldlog.dll On x64 Version of Windows 7 this is located in
C:\program files (x86)\Windows Live\Shared
In x86 version it would be
C:\program files\Windows Live\Shared
Save a copy of the dll just in case. Right click on the dll and choose Copy. Now go to desktop and right click an empty area and choose Paste. This will give you a copy to copy back in case of any problems. Now delete the wldlog.dll and Try and launch messenger. If no fix, just copy the wldlog.dll back to it's original location. Let us know how it goes. If you'd like extra assurance, create a System Restore point before you start: System Restore Point - Create