Sometimes with Norton, you need to remove & re-add firewall exceptions after updates to either Norton or the particular program such as FW. Make sure it allows exception for both TCP & UDP.

If there is more than one FW being used on the network, make sure neither the listening or connection ports are the same; routers will reserve one port per computer & per application.

Try suggestions here, especially replacing the gnutella.net file: If LW 4 Will Not Connect (click on the blue link)

The instructions on replacing the gnutella.net file are same as LW, except of course the folder is called FrostWire. An old sample image of how to find FW prefs folder: FrostWire Preferences folder (click on link). (That sample image is for deleting the FW prefs folder, however it does at least show you how to find the folder.)