[paul9]

I'll give you £20 for it.
It sounds like the same sort of thing that used to happen to Gameboys and Nokia phone screens, where there is a special conductive rubber strip to take the electrical signals from the ribbon cable to the conduction paths on the glass of the screen. This strip may not be making full contact with the screen or ribbon cable. It should be repairable, if that is the problem, but a bodged repair can make it worse.