Is your LW connected properly (how many green connection bars do you see)? If there's a connection problem, check here.
Connection problems? Check here first!
And tell us your system details.
System details - help us to help you

If you are connected, see this thread.
Problems with the search

If that doesn't help then delete LW's preferences folder when LW's properly closed. See point 3 below (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 LW's options, you'll have to go back through & reset things afterwards