I also got this Microsoft Surface Pro Black Screen problem and I was able to fix it by following the instructions in this video: https://www.youtube.com/watch?v=Tw6zSHBl...
I had the same problem on my Surface Pro 6. I then fixed it by removing the screen and disconnecting the battery and connecting it again. It worked, but sadly I managed to rip the digitalizer cable. But I’m happy that it works.