If you have Adobe Digital Editions installed on your computer you should be able to open that while your PE is "mounted" (which it is if the pulldown notification says click to turn off) and see the eDGe as a drive within ADE. Then (within ADE) you can drag books across to your eDGe.
The "someone else is using the book" message usally means an Adobe disconnect of some kind. If your Adobe registration is different on your computer from your eDGe you would need to make them the same. If they are the same I don't know what to tell you.
First thing, I suppose, is to check whether your library book shows up in ADE on your computer (I'm sure it does, doesn't it??)
Oh, and hello and welcome!!
