How about deleting your LW preferences folder, using the Start menu -> All Programs -> LW -> Uninstall, thus removing LW. Then re-installing LW 4.16. Remove & re-add firewall exception to your XP firewall. May need to again put in a fresh gnutella.net file.

In User name\AppData\Roaming\Limewire replace the Gnutella.net file and hopefully that will work.
This happened to me after Vista/Win XP automatically updated with the new Service Pack 3 last week and when I replaced Gnutella.net everything was back to normal.
To get to the App Data folder you will have to go into the Control panel and the section "Folder options" and in the view section change the "view hidden files and folders" to approved so that you can see the App Data folder in the "User name" section of your files.
You can thank Lord of the Rings for this advice as it worked perfectly for me after I had tried everything else to try and solve this issue.

I was gone for the last few days, I didn't try any of these things, and starting today, I now have full connection again. I don't know what the deal is. If it happens again, I'll have to try some of these things you guys suggested. Thanks!