Is LW connected properly (all green/blue connection bars)? If you're connected, try these fixes.
1. In LW go tools > options > searching > basic & check whether the 'show license warning' box is ticked. If it does, untick it > Apply > ok...see if that makes any difference.
2. Delete 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.
For any Vista users:
LimeWire Pref Folder in Vista
3.
Problems with the search
If you're not connected:
System details - help us to help you -> Provide these details when you post!!!