I would probably first install Kobo Start Menu and/or koreader/KoboLaucher to see whether a different software has the same issues. Or maybe faster: Full factory reset will reinstall an earlier Kobo Nickel firmware.
I don't see any way an unopened AuraHD could somehow get its ribbon dislodged. I can easily see how some particular way of holding the reader--clasping it in your hand on one side-- could for some unlucky owners result in a broken screen.
A new screen would be cheaper than an new reader and it is available on AliExpress: Somewhere around 52€. (
Here!)