Thanks for the tip Davidfor, I tried to reset, and the third time did it!
On the kobo-help web-page shows this way:
Before you perform a manual factory reset, charge your eReader for at least three hours. While your eReader is on, remove the port cover on the bottom of your eReader. Insert a paper clip into the small hole next to the Micro USB slot and push gently. You'll feel a click and your eReader will reset itself. When you see square icons on the screen, insert a paper clip into the small hole next to the Micro USB slot and push gently. Repeat step 3 two more times. Your eReader's screen will turn black, and show a Critical error message. Don't worry, this is normal. Tap the check mark icon at the bottom of the screen to reset your eReader.