I don't think the LW 4.0 was UPnP capable. I'd need to check. If that's the case you will need to port forward your router. I had a similar version.
You will need to set up a static ip first: Computing & Information Technology : University of Vermont
Then see http://www.gnutellaforums.com/connec...4g-router.html which should be similar to yours.

If LW was working fine before then try deleting the LW prefs folder whilst the program is closed; found here: Macintosh HD/System Folder/Preferences/.limewire
List your prefs folder in List mode & you should find it at the top.