Providing LW is properly connected to the network:

1. LW 4: 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: In LW go tools > options > security. Click on the Settings button, next to Warning Messages > untick the box referring to license > ok. Click ok on the main options page.

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. LW 4: Disable all options (TLS, DHT, UP capablilties) within LW's tools > options > advanced > performance. Click Apply > ok to save the change.

LW 5: In LW tools > options > advanced > super really advanced > performance. Disable ultrapeer capabilities, connecting to DHT & also TLS > ok.