Norton 360 includes a firewall. So if you're using the Norton firewall, you need to make sure that the Windows firewall is off (2 software firewalls will conflict with each other & neither one will work properly).

Once you're sure that Vista's firewall is off, try reconfiguring Norton's firewall. Remove all rules for LW & add them again from scratch. Check the threads below for more info.
PortForward.com - Free Help Setting up Your Router or Firewall
http://www.gnutellaforums.com/226610-post6.html

If that doesn't help, try the fixes here: If LW Will Not Connect
If you've only just started having probs, the first things to try are deleting/replacing the gnutella.net file & deleting LW's preferences folder. After that, try all the other fixes...they've all worked for different people - sometimes it's just a matter of finding which fix works for you

Otherwise, you could try port forwarding for the 2wire. The instructions are here: Port Forwarding for the 2 Wire 2701HG-G
LW's listening port, port in the 'manual port forward' box & port forwarded within the 2wire config all need to be the same number