Make sure that your Windows firewall is off & configure McAfee to allow LW.
Port Forwarding for the McAfee Security Center

Which OS are you using? Which version of LW & Java? Do you use a modem and/or router (there are firewalls within most routers & some modems)? What's the brand & model number? Who is your ISP? Where are you trying to connect from? It would've been really great if you could've answered the questions from my system details link.

Delete LW's preferences folder when LW's properly closed. See point 3 here & also point 2 if you've used much older versions of LW in the past (there could be a folder in either location).
Fixes for LimeWire

I don't know what version of Java you're using, but if you have Windows XP, you could try reinstalling this Java. Use the JRE offline installer. Remove your current Java version before you install this one.
Java SE Downloads - Previous Release - JDK 5