Nikon 5700: Monitor and viewfinder flicker

The problem started several days ago when I turned my Nikon 5700 on.
Monitor and viewfinder were flickering so much that I couldn't see the
image. I played around with the controls (power on-off, zoom in-out,
etc) until I thought the problem was suddenly fixed. Unfortunately it
was not fixed. There is random unpredictable flickering which shows on
the photos I take.

Your help will be appreciated, especially if you had a similar problem
with this camera.

thanks
Anthony