It's very simple to delete the LW preferences! Do a search for .limewire & delete it from the results. See: Fixes for Limewire It's location may depend on your operating system also. But only do it whilst LW is closed! You throw away the entire folder!

For firewalls see: http://www.limewire.com/english/content/firewalls.shtml

topbrewer: Do this simple test for us. Using your browser go here: http://www3.limewire.com:6346/ The page should say 'Your test worked!'. What happens when you go there? If you can't reach that page then something's blocking your access for LW.