There is a ribbon cable located at the bottom of the monitor that may have come loose. I can't say that I have seen this in the past however. More likely, the solder connections for the connector have degraded a bit and require a re-flow. If you can solder, you should be able to resolve this by yourself. Carefully open up the unit (unplugged of course...) and look at both the ribbon cable and perhaps re-seat it as well as the solder connections for the connector itself.
Let us know what you find.