Delete LW's preferences folder. See points 2 & 3 here.
Fixes for LimeWire

Which version of Java are you using? Try Java 1.6. Use the JRE offline installer & remove your current Java version before installing the new one.
http://java.sun.com/javase/downloads/index.jsp

Which software firewall are you using & which OS? Don't forget that Win XP & Vista have their own firewall. Rather than running without a firewall, configure it (just one, 2 firewalls together will cause problems) to allow LW.

If you're still stuck, please give some details.
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