Did LW ever work well with Java 1.6.0_02 installed? That version works fine for me but some people have had problems with it. You could try this older version of Java & see whether that makes any difference. Use the JRE offline installer & remove your current Java version before you install this one.
Archive: Download Java 2 Platform Standard Edition (J2SE) 5.0 Update 11

It wouldn't hurt to delete LW's preferences folder when LW's properly closed. See point 3 here & also point 2 if you've used older versions of LW in the past (there could be a folder in either location).
Fixes for LimeWire
This will kill all of your settings within options, you'll have to go back through afterwards & reset things. If you're not sure of your settings, go through LW's tools > options & write them all down, so that you can reset things later.

These instructions should help you to set up port forwarding.
Port Forwarding for the Dlink DI-524
As LOTR said before, don't forget the step of setting up a static IP first LW's listening port, port in the 'manual port forward' box & port forwarded within the router all have to be the same number.

This will explain a bit more about a static IP address
PortForward.com - Free Help Setting up Your Router or Firewall