Did you configure your firewall so it allows LW full access (advisable not to have 2 active firewalls b/c they can interfere with each other); Firewall configuration instructions (click on link)

Can you give us a total desciption of your set up:
1. OS version? (eg: Windows 98)
2. What firewalls you have?
3. Connection type? (eg: broadband, cable, etc.)
4. Modem & router brand name & model numbers?
5. Where are you trying to connect from (home, school, work, etc.)?
6. What version of Limewire (LW) & Java do you have? (Go to LW's menu Help>About LW...) Will show both LW & Java version.
7. 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?
8. Are you sharing the connection with other computers or p2p sharing programs? If yes, please give details of set up.

BTW it's my guess it's an issue with your modem/router. So please give details about this.