Why isn't Windows Live Messenger working and how can I fix it?

Hi, over the past couple of days my Windows Live Messenger software has stopped working. It'll spend ages saying 'signing in' and nothing will happen. Eventually it'll stop and after a long time, a message will come up saying 'Windows Live Communications Platform has encountered a problem and needs to close.' The internet is definitely working, as I'm still able to go onto websites. I've tried uninstalling and re-installing it, but it's still not working. The Connection Troubleshooter test also says everything's working fine, which it clearly isn't.

Any ideas?