Most Downloadable Audiobooks come in multiple files. In order to receive the complete Audiobook, you need to wait until all the files are downloaded, you can check this by clicking on the "show files" option of your app's menu.
The most likely cause is that your device has not been authorized by your Overdrive Account or your Adobe ID. Verify this by selecting Settings or Account from your app menu, or by selecting Authorization Information from the Help menu of Adobe Digital Editions on your computer (in the case of E-readers).
There are various error messages you may encounter, requiring different solutions. To find the solution, access http://help.overdrive.com and search for the specific error message in question.
If you have an appointment at the library to learn about using E-books and Downloadable Audiobooks, you will need your Ottawa Public Library card, the device(s) you are using, and the relevant power cords. If you have an E-reader, you will also need the USB cable and computer (laptop) with which to you connect your E-reader.
If you have updated the system and the app is not working, the app may need to be updated as well. Check your app store for an update. If the app is updated and not working, try shutting down the device completely (not sleep mode) and restarting it after half a minute. If this does not work, you may need to delete and re-install the app on your device.