After you deleted LW's preferences folder, did you have to go through LW's setup wizard next time you started LW?

Find your gnutella.net file, hover your cursor over the file - what size is it?

When you were port forwarding, did you make sure that LW's listening port, port in the 'manual port forward' box & port forwarded within router setup were all the same number?

Try downloading LW 5 - apparently that doesn't need the gnutella.net file to be replaced if there's a connection problem. Don't worry if you don't want to use LW 5, you can easily revert to 4.18.8 again It's worth trying the newer version to see whether it connects.
There's a link for download within this post (click on link): http://www.gnutellaforums.com/333278-post2.html
Go through steps 1 - 8 in that link, even if you've tried some of them before.

And here's a link to download 4.18.8 again if you want to: Lime Wire » Download Out-Of-Date Installers