The contrast adjustment screen appears all the

Sounds to me to be either a failing button position replacement spring in the button itself. This problem also could be caused by dirt buildup surrounding the hole in the monitor bezel where the button protrudes. Try using a dental tool or something small and pointed to clear any possible debris from the buttons edges. Also some canned air may help. If these things don't fix your problem the bezel may need to be removed for a more thorough cleaning. If you are able to make it dissapear by pressing the button it most likely isn't hardware failure causing your problem, as those buttons are rarely used.

I hope that this helps fix your problem.

Good Luck