If you can't open a book...

[Reader Paradice]

...this might be one of the reasons;

If you let's say downloaded a book as a preview on your Vox or Touch, and then decided to purchase the book, and it starts to download, it might try to overwrite the preview and you end up with double files of chapters, which forms a corrupted download. If you try to open the book, it shows that it is loading, but then does not move past the opening page. In effect, it does not 'open'.

If this happens, delete the book off of your device. Then,...sign into your account and go to your PURCHASED BOOKS LIST. Check off any of the books you deleted from off of your device and then press BOOKMARK. This will reload your purchased book and sync it to any device or computer that you have the Kobo Desktop installed on.

This is also what you would do, if you deleted a purchased book by accident, or having deleted it by choice, decide at a later date to reload it onto any of your devices.....