Do you need to use a proxy to connect? Sometimes you need to change the proxy you use. And then keep changing until you find one that works.

I know you said you configured your firewall but just to double-check: http://www.limewire.com/english/content/firewalls.shtml

Try deleting your LW Preferences folder whilst LW is closed; instructions here: Fixes for Limewire

If still problems post back with the followintg details.
Can you give us a total desciption of your set up:
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?