You're off topic for this forum, which is dedicated to Windows Live OneCare.
Customer service is available for paid subscribers via phone in some regions - http://support.msn.com
Windows Live Hotmail support - http://support.live.com (via email for all users)
The first thing I'd recommend, though, is to check your PC date and time. If that is correct, this may help: http://messenger-support.spaces.live.com/blog/cns!8B3F39C76A8B853F!12862.entry
-steve