A switch on the back of those reels that don't move is either dirty or misaligned. Use the other ones that reset as a guide to help you figure out what is normally open/closed at the 0 position. A switch should also close at the 9 position. There is a little plastic arm that moves up and down to actuate the switches.

Yes - perfectly fine, but when you score points on that reel you'll have to manually reset it until you fix it.

There is a little metal tab/bar/doodad you can push in under/on the side of the score reel and pull the whole unit away from the metal "shelf" it's sitting on. You should then be able to use a regular sized screwdriver. It's like a little prehistoric locking mechanism.

I'm sure if you describe the issue we can at least help point you in the right direction.