iTunes Store: download

I downloaded an album a while ago but one of the songs is showing as not downloaded even though it is in my library and plays. The issue is on the iTunes Store app on my iPad. On the 'Downloads' tab, there is the red circle with a 1 in it. When I click on it, it shows the song with the word 'Waiting' underneath it. Nothing happens when I click on the song and if I try 'Edit' at the top, it moves to the right as if a 'delete/clear' button should appear but nothing does. I've deleted the iTunes Store app and reinstalled it, rebooted the iPad and generally followed all other instructions. Anybody got any ideas?