I’ve had an issue appear twice now, where my main screen is black, the keys light up, I can connect an external display, but can’t recover the main screen – it’s just black, no loading logo, nada.
I tried all the NVRAM resets, and other tricks you can find on google – doesn’t help.
The first time I fixed it by taking it to the Apple Store, and they told me exactly what they did.
They opened the MacBook, and unplugged a cable, that’s near the escape key, and plugged it in again.
If you don’t have the star-shaped key, I’ve since discovered a quick-fix, simply by pinching together the top-left part of my macbook’s keyboard, about one to two inches in from the edge, it pushes the cable back into place – hey presto problem solved.