Why won't my iBooks download on my iPad after the iOS7 update?

Every book I ever purchased or downloaded is frozen in a "downloading" status, but none of them ever starts downloading. I connect via wifi and everything else I had has downloaded (my music, etc.) but all of my books are unreachable. It is really frustrating because I was in the middle of one and can't get to it! I am not an Apple expert, I don't have an iPhone, just an iPad, so keep it simple for me please!