Try to switch to a higher port (listening port), something like 64049, 65255, 47058, or their like.
Your ISP might only block the ports 6346,6348, etc......
In LW go Toos>Options>Advanced>Firewall Config....
On how to config. your firewall to let those ports pass, read here:
http://www.gnutellaforums.com/showthread.php?t=51361 