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.

In LW, file > disconnect. Wait 5 minutes, file > connect.

When you set up port forwarding, did you make sure to set up a static IP address first (won't work, otherwise) & did you use these instructions?
Port Forwarding for the ZyXEL X-550
Are LW's listening port, port in the 'manual port forward' box & port forwarded in the router all the same number? They should be.

I can't find any info to suggest that your ISP are anti-p2p. If those 2 earlier suggestions don't work, try changing ports. Tools > options > advanced > firewall config. Change LW's listening port to 64049 (or try others in the range of 49152 - 65535). If you do change ports, remember to also change the port number in the manual port forward box & port that you've forwarded within your router.

Is Java 1.5.0_11 the only Java version that you have on your computer? Go to add/remove programs & check. If you've got others there, remove them. Then restart the comp & see if LW connects.