iOS7 crashes when downloading on iPad 2

I've pressed "download and install" and I've accepted the terms of condition. It completed the preparation, then the apple screen comes on with the bar saying how far it's done. It gets about half way done (bearing in mind this has took half an hour) then crashes, and takes me back to my original lock screen, and nothing has changed. I've tried to download it again, but it has done exactly the same thing. Help!