One day you just click on the Live Messenger Icon and it won’t start up, what the heck? You check the task manager and you see it’s still running, in fact if you click on it various times it runs as many instances. What the heck is going on here? You think it might be a virus. You re-install, scan your computer for viruses/spyware, nothing.
After a while of searching, I found it has to do with your router. Live Messenger fails to load due to firewall exception errors with your router. Most people who had this problem had D-Link routers. Some solved it by simply reseting their router, but for some that didn’t work. Instead they discovered that they also had to turn off UPnP Settings. Turning this off consequently resets the router as well. Once it’s back up, you’ll be glad to know that Live Messenger now works fine.
Source: MSDN Forums
