If you have a gen 1 printer then check J8 on the board in the back, if it is gen 2 or gen 3 then check J7. All of those plugs on the computer in the back are crap, they ahve a tendency to spread and make poor contact. You need to pull the plug out and look into it, the holes that go over the pins spread so they do not touch the pin. You need to squash it a bit so it grips the pins tightly. I do this with a hypodermic needle. Do not go berserk.