Looks like the batteries aren't retaining memory. Did you cycle through your switches on the coin door? That can get it out of factory reset so you can coin boot.

In the pinball world, Black Knight is both iconic and addictive. There were times I had a hard time pulling away because of how addicting those drop targets are. I also liked the spring/switch at the middle ramp that you collect points from the inlane.
It's a game on my want list for someday, but I won't be able to beat the price I paid for my last one ($100, playfield and backglass were mint and only needed a $15 rom)
Good luck and enjoy!

When you push any of the coin door test switches, what do they do? Does anything change on the displays? It should, and if so, you will be able to cycle through until it gets to attract mode (ready for a game)