If you are experiencing problems (e.g. blank pages, pages not appearing to load properly) with reading ProQuest ebooks in Adobe Digital Editions after downloading them to your iPad, ProQuest suggest changing the display settings within the book to either a black or a sepia background. You can find out how to do this here.
If this doesn't work, you can also try using a different iOS app that supports Adobe DRM, such as PocketBook Reader.