kobo aura one display problems

Hello
I own a refurbished (no warranty) kobo aura one since less that one year. No problems since a couple of days ago: the display appears in this way




what is readable is in the small rectangle on the right.
I made both the factory resets, via menu and manual, but with no result.
Please suggestions?
Maybe changing the os and installing an open source OS, if exist, for kobo aura one?

Thanks in advance

Rob