Does not move I mean.

You have to get all the game pieces in the previous levels

We have the same issue. Scooby just digs at the ground and indicates we need a red book. Watched a youtube video and the person simply walks up and the book is placed on the shelf, without doing anything special. I don't get it. Some sort of glitch in the game maybe.

What do I do if one of my keys don't show up?

To beat the pumpkin head guy on the horse: You have to pull the levers on both sides so the gates are both open at the same time. The plane flies in and drops something and while the pumpkin head guy is confused, he is vulnerable to your weapon. You must hit him 3 times total.