Do you mean that no search results appear at all (ie the page is blank), or the file you're looking for doesn't appear but other stuff does?? Is your LW connected to the network properly (all green connection bars)?

If the search page is blank, try this: Problems with the search

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.

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.
LimeWire Pref Folder in Vista