Is your LW connected properly (all green/blue connection bars)? If LW is connected, try the fixes below...they're things that have helped other people.

1. In LW go tools > options > searching > basic & check whether the 'show license warning' box is ticked. If it's ticked , untick it > Apply > ok...see if that makes any difference.
LW 5 users, check this link for info about the license warning: http://www.gnutellaforums.com/338001-post3.html

2. Problems with the search

3. 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 change all of your settings within LW's options, you'll have to go back through afterwards & reset things to the way you like them.
Vista users: LimeWire Pref Folder in Vista

4. Disable all options (TLS, DHT, UP capablilties) within LW's tools > options > advanced > performance.

If none of those things help, run the condi program mentioned in this thread (click on link) & send the log file to mrogers: http://www.gnutellaforums.com/335648-post19.html
There's more info about condi here: Connection Diagnostics - LimeWire

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If LW is not connected, try the fixes here: If LW Will Not Connect
If nothing there helps, post back with your system details