Old and new displays won't switch on after attempted repair

Before buying a new motherboard I would try cleaning the connector points with a soft bristle tooth brush and a small amount of rubbing alcohol, I’ve had that problem with some phones and that dos the trick, make sure it’s dry all the way before re connecting or powering back on it won’t take but a minute to dry or evaporate, also try to plug it in for a sec and power on maybe try with a different cord, just a thought