Then check on one thing.
You see: Even though they have shown up on your Library screen by now, you still might have become disconnected from the network since they showed up (and they would still show up there, I think...)
The thing to check on is: Do you have a good network connection at present?
If so, if you're sure, if the signal strength bars are in the four or five-bar range, then try downloading just one of the three books, as a test. (If it works, then try the other two.)
What result do you get that way? if there's an error message, please record it, or take it down, and then pass the error message on to me, so that I can tell what's going on, or what is failing to happen, and perhaps, why it fails.