Yes I'm pretty sure the firewall icon has always been there.

By the way, i left the computer by itself for about an hour and i came back and it said it had a fair connection but then disappeared.

I might be able to find out what modem/router it is but i'm not sure how to find it. Am I able to look for it on the computer or do I physically have to look for it?

And I changed the listening port number thing and it didnt do anything.

Go to the main computer & have a look at what's plugged into it. The modem might be on the roof, I'm not too sure. But it might be inside, connected to the main computer. A router should be plugged into the main computer.

Does the main computer belong to someone else? If there's a problem with a modem or router, you should talk to whoever owns the main computer...if you need to go making any changes to the setup, they should know about it

Does anyone use LW on the main computer? If so, can they connect? Have you tried using any other p2p?