I've already opened a port and changed my firewall settings to allow limewire through but everytime I attempt to download, it just says "Connecting (XX hosts tried)" and continues to say this until it attempts a connection with all possible hosts and then says "Needs more sources". When I first got limewire it was fine, the default settings allowed me to download but all of a sudden last week it started doing this. Can someone give me a hint, please?

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 movie & program files before download). If a file has heaps of sources but no Bitzi rating, chances are it's a fake.
Fake files showing up in search results
How to find music

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 changel 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.
In case you're using Vista: LimeWire Pref Folder in Vista

You were absolutely right! Thank you for the very detailed response, it works fine now.