MSN and Wireless...

Hi,
Well I recently got wireless and everything is working fine on my computers (Vista Laptop and XP Desktop), such as my internet and my Wii and DS connection, but my msn isn't When I go on it I don't receive peoples messages and they don't receive mine but theres no usual "could not be delivered" message its as if it just stops. People have said that my router could have an inbuilt firewall which could be blocking msn from working properly, but I have no idea how to find out if I have got one or how to stop it. My router is a Belkin and it never disconnects if that's any help? I don't know much about computers or wireless so I have no idea whats going on. Thanks in advance to anyone who can help me.

Emma