There are quite a few threads around about this problem, here are a couple

http://www.gnutellaforums.com/showth...net+connection
http://www.gnutellaforums.com/showth...net+connection
http://www.gnutellaforums.com/showth...net+connection

Try some of the suggestions in these threads. You can always use the search (top right) to look for more