Try deleting 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.
LimeWire Pref Folder in Vista

Did you remove all other Java versions before installing 1.5.0_11?

A couple of people have had success after uninstalling both LW & Norton, then reinstalling LW & last of all reinstalling Norton (this is a fix for problems with ZoneAlarm but it's also worked for Norton).

Are you connecting from a house? Can you check if there's a router in another room?