WordPress scrolling problem

Hey there. This is going to be hard to explain, but the problem is on one of my sites, in the editor when making a new post, there isnt a slider thing on the right to scroll down through the post. I have to go to the far right and scroll down the entire page. Does that make sense? On my other site i can just scroll down through the new post im writing. Anyone have this issue? Or is there some option im missing to turn on?