Try the fixes in the thread below. There's info there about how to reconfigure the Norton firewall. Double check that the XP firewall's off - that will conflict with Norton.
If LW Will Not Connect

Start off by
1. Deleting/replacing gnutella.net file.
2. Deleting preferences folder.
3. Changing port numbers.

If those don't help, go through the rest of the fixes in the help thread.

You could also try port forwarding for your router. The instructions are here: Port Forwarding for the Linksys WRT54Gv4
You'll need to set up a static IP address first: PortForward.com - Free Help Setting up Your Router or Firewall
LW's listening port, port in the 'manual port forward' box & port forwarded within router config all have to be the same number

Tiscali are well known for causing problems (connection & download) with LW - yes, sometimes out of the blue when the user's had no problems in the past. Use the forum search to look for Tiscali & you'll find lots of info