Try the suggestions in this thread:
http://www.gnutellaforums.com/showthread.php?t=53828
If that doesn't help, post back with details of your setup.
1. OS version? (eg: Windows 98)
2. What firewalls you have?
3. How much ram?
4. Hard Disk space available?
5. Connection type? (eg: dialup, broadband, cable, etc.)
6. Modem & router brand name & model numbers?
7. Where are you trying to connect from (home, school, work, etc.)?
8. What version of Limewire (LW) & Java do you have? (Go to LW's menu Help>About LW...) Will show both LW & Java version.
9. Who is your isp provider (Internet Service Provider)?
10. Are you sharing the connection with other computers or p2p sharing programs? If yes, please give details of set up.
11. Is this a your 1st try at LW or is this a new problem with an experienced user.
12. 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?