Do you mean that you've upgraded to LW Pro from basic?? Have you ever been able to download files? There are heaps of fake files throughout the network & these typically have lots of sources but will sit connecting for ages & then get stuck needing sources forever. Check out the threads below for info & tips (make sure to use Bitzi to check files before download).

Fake files showing up in search results
How to find music

However, if absolutely every file needs more sources (even old songs with a single modem source), try this: 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. If you're not sure of your settings, go through LW's tools > options & write them all down, so that you can reset things later.