Your school is probably the issue. Too many schools nowadays deliberately block p2p sharing. It uses up too much bandwidth which they pay lots of money for.
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?

A good idea to only have one firewall active since they can interfere with each other: http://www.limewire.com/english/content/firewalls.shtml