On board / internal display works intermittently / randomly Macbook Pro Mid 2012. Original board and display. About 2 months ago, laptop screen cuts out. External display used to prove everything working normal, including passing Apple Hardware Test. Take to store, conclude the "display is dead", but all logic board components functioning correctly. Take home, hook up to external display, use for a week - then, randomly, the laptop screen starts working. Works until I reset laptop, stops working. Tried all different configurations of plugging in external monitor / power cycling / diagnostics / PRAM rest/ display resolution changes / external display change while power cycling to try and trigger the laptop screen to work again. Fails. 2 days pass - laptop boots up with screen on! Alas I'm forced to restart, and it goes away again. Then comes back in a week. Then I have to power off... and its gone. I'm currently at gone. I don't know what to do - it seems like I either have to buy another display and hope that works properly or replace the logic board, which I can't afford. Displays are ~$78 on ebay. Ideas? I'm about to conclude that it's a poltergeist and I should just pawn it off as a possessed artifact(jokes)
I see you tried resetting the NVRAM (PRAM), but have you tried resetting your SMC?

For your model, the steps to do this are:


Shut down your computer
Keep the MagSafe adapter (power cable) plugged in.
Press at the same time shiftoptioncontrol (on the left side of the keyboard) and the power button
Let go
Turn your computer back on with the power button.


Let us know if this makes any difference.