I really sympathize with you, your problem is all too familiar to me!
The only thing that I can tell you is that the Kobo reader I bought
originally, stopped working completely; I sent it back for warranty repair /
replacement, and the new unit they sent back has worked perfectly. My
original Kobo reader would not open downloaded library books; the new unit
does without any difficulty.
I am using a Kobo Aura HD. I think that their quality control must not be
very good, but how can we be sure? I know Adobe won't let me open any books
I had on my old Sony reader. To me, Adobe is stifling our right to buy and
read any books we want to.
The user forum in Adobe has complaint after complaint from people who are
locked out of the books they have bought, due to Digital Rights Management.
This must be hurting the purchase of new books; why buy a book and take the
chance that you won't be able to open and read it, when you can download
books to borrow from the library that don't cost anything.
If I were you I would contact Kobo about getting your reader repaired or
replaced. The fact that mine worked after Kobo sent me a new unit, tells me
that the problem was with the reader. However, Adobe makes me very angry.
I wish we could start a class-action suit against Adobe.
Good luck with getting your problem solved. Please tell me how you are
doing with this!