No picture on screen but backlight and sound present

We have an issue where our tv will go period of time not working then will work fine for a couple of days.

It has no picture but has backlight present and sound. When watching the tv it will blink and create a couple of horizontal lines before blacking out.

If we do not use it for a few days or weeks then it will magically start working again randomly.

We have tested incoming AC, DC output and the backlight but are not sure what’s next?

Cheers

Martin