I still have an old Toshiba laptop that I don't use much anymore that was having the exact same problem. I plugged in a VGA cord to a projector and both screens are working correctly after that. I also freed up the right hinge that had come disconnected from the base by breaking some plastic away from it. There is a wire that goes through there, maybe it was kinked or half broke because the hinge isn't in the right spot. I did both of these things at the same time, so I don't know which one fixed it, but I suspect it was plugging in the VGA cord to an external video display.