I'm not too sure about this one
LW 5 doesn't have any 'resume' function like LW 4 - incomplete downloads should resume automatically when sources are found. And even if the downloads are stalled, they should still show up in the download tray at the bottom of LW's page.
In LW click on View & make sure that you don't have 'hide download tray' ticked.
If you click on 'Show All' do you see any incomplete downloads?