Yahoo messenger and Windows Live Messenger wont connect on Vista

This is recently installed Windows Vista Basic based Acer Aspire 5050. Everything is working fine of this except Live Messenger and Yahoo IM. Though my Internet is working fine, I am not able to get online on these instant messengers. However when I try connecting with Trillian, I can do it easily without any problems. Later when I ran live messenger diagnostics, it says my firewall might be blocking the connection and the issue is something related to Key Ports.

But as far as I can see it is already allowed through my Firewall. Now the problem is I don’t know how to open port 1863. Can someone please help me.

Try turning off Firewall once and see if you are able to connect Yahoo and Live Messenger. If it is working fine than make settings respectively in your windows firewall and if it is not working then better download and install some third party firewall.