Horizontal lines (bottom half of screen that flicker constantly)

TV has never been knocked etc, turned it on this morning and the bottom half of the screen has black/ grey lines that shift/flicker but only the bottom half of the screen.

Top half is still perfectly clear. You can occasionally make out a little bit of the bottom but at this point it's unusable.

Ribbon cable has already been replaced but didn't fix (at suggestion from local technician). Tried hard reset and default settings to no avail.

When ribbon cable is removed, screen doesn't flicker.

Any suggestions?