Horizzontal line on the screen. Freebok model

Hi!
I have a recently bought freebok, and in the past few days a horizzontal line has appeared on the bottom of the screen.
I have already tried uninstalling,updating to the latest version the graphics card driver but the line remains. It didn’t take any hits.
I realized that by taking a screenshot the line doesn’t show…
What can I do?
Thank you.