Don't use the Windows & Norton firewalls together. Disable the Win firewall & configure Norton firewall to allow LW.

Your modem doesn't have a firewall. Are you using a router as well?

Some XP users have had problems with Java versions 1.6.0_01 & _02, only a couple of Vista users have had to change Java versions but you could try this version instead (if it makes no difference then it's easy enough to reinstall the latest Java!). Use the JRE offline installer & remove your current Java version(s) before installing this one.
Archive: Download Java 2 Platform Standard Edition (J2SE) 5.0 Update 11

You could also delete LW's preferences folder when LW's properly closed. See point 3 here.
Fixes for LimeWire
This will kill all of your settings within options, you'll have to go back through afterwards & reset things. If you're not sure of your settings, go through LW's tools > options & write them all down, so that you can reset things later.
http://www.gnutellaforums.com/genera...der-vista.html

Windows Firewall is disabled. Only Norton's Firewall is working and I've changed the programs settings to allow LW.

I'm not using a router.

I've changed the Java Version, as you recommended. The new version is 1.5.0_11. Still not working...

I'm gonna try to delete LW's preferences folder and I'll let you know what happens.
Thank you very much.