All I see is a spinning wheel when I try and download my iBook, my iBook stopped downloading half way through.

The spinning wheel means that your apple device is downloading the ebook. Please be patient as some books may take between 5-45 minutes to download depending upon the size of the file. If you continue to see the spinning wheel, exit the iBooks app and try to download the iBook again.  Please contact their support team at 1-800-275-2273 if you need additional help.