In LW go tools > options > downloads. Make sure that your maximum downloads aren't set at zero

If that's not the problem, try LOTR's advice in this thread.
What is Queued?

If you delete the preferences folder, make sure that LW's properly closed first. Remember that this will change all of your settings within LW's options...you'll have to go through & reset things afterwards.
And in case you're using Vista: LimeWire Pref Folder in Vista