Is your LW connected to the network (how many green connection bars do you see)? If you're connected ok, try this: Problems with the search


And if that's no help, delete LW's preferences folder when LW's properly closed. See point 3 here & also point 2 if you've used much 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.