Hi Nursebelle,
I've got an article here for you that can help you find and re-download your past purchases:
Downloading past purchases from the App Store, iBookstore, and iTunes Store
http://support.apple.com/kb/ht2519
You will want to verify that the purchase you are wishing to re-download is in the purchase history of your iTunes Store account, then delete it from your library and use the steps in that article to re-download it. Thanks for being a part of the Apple Support Communities!
Regards,
Braden