Are you sure that you deleted the preferences folder properly? It's just that deleting that folder has fixed this problem for quite a few people. Remember that LW has to be properly closed before deleting the prefs.

Try the latest LW Beta version (4.13.14) & see it that behaves any differently. You'll find a link for the Beta download on the usual LW download page.
Lime Wire » Download LimeWire

What version of Java were you using when things were working well? Some people have had problems with Java 1.6.0_01...you could try using this version of Java instead. Use the JRE offline installer & remove your current Java version(s) before you install this one.
Archive: Download Java 2 Platform Standard Edition (J2SE) 5.0 Update 11

If that doesn't help & you want to go back to Java 1.6.0_01, find it from the list of archived versions here
Archive: Java[tm] Technology Products Download