You could try changing ports. In FW go tools > options > advanced > firewall. Change FW's listening port to 65000 (or a port in the range of 49152 - 65535) > apply > ok.

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?

Check out this link for info about configuring Windows firewall. It's referring to LW but it's the same deal for FW. firewall:User Cant Connect - LimeWire

Your school might be stopping you from connecting. Lots do. Can other people at school use p2p apps?
You might need to check with the school - to see whether they'll let you use p2p