Hi.

First candidate would be a blown fuse. There are a few tiny surface mounted fuses near where the display ribbon cable plugs into the mainboard. It is very common for one of those fuses to blow as a result of plugging in a cable off-by-one-pin. We've just about all done it at some point.

Stick an ohm-meter across each of them in turn. Whichever one does NOT show zero-resistance is the blown one.

Cheers