Ereader switches off

Ive downloaded a first ebook on my Daylight Computer which appeared in Ereader. But from that moment onwards, earader switches off immediately when i open it. I deleted the ebook already from the device but the app still shuts off immediately when opening. I cat deleted the app itself because it belongs to the app “of the . I tried “forced shutting off”, an option at Settings but this also isnt making a change. What to do?