These original posts are 9 years old but I resurrected my 2011 mac. I must have gooched this little vertical sync cable when i removed it. I stripped it down by gently pulling back the tiny plastic tabs holding the wires in the connector. I didn’t do anything special, just jiggled them around a bit (that’s the technical term) put them back in again and lo and behold it worked. Thanks you for giving me the idea to do this people.