First thing to try is to delete the LW preference folder as described in this thread:
Fixes for Limewire when LW isn't operating as it should
If this doesn't fix it, uninstall LW and all Java on your computer. The downlaod the JRE offline installer of the newest version (1.5.0_07) from here:
http://java.sun.com/j2se/1.5.0/download.jsp
Make sure that you reboot after uninstalling and after new-installing of Java before re-installing LW also using the offline installer.exe.
