I have the same problem. I tried to replace my keyboard on my 2012 A1286 15 inch and got stuck as I discovered the screws on the wifi bracket above the DVD drive were damaged. I could not get them out so I reassembled the macbook. The screen did not turn on, so I opened it up and checked the Dlvs cable, I unplugged it and plugged it back in, but still no screen working. I equally tried the control shift option keys.
does this mean my cable is damaged? or could there be some debris on the connectors? The MB was very dusty when I opened it and I gently removed the dust by hovering the vacuum cleaner over it. I equally used a super soft brush ( make up) to brush.
What are my options now?
Shelly