Generation 4

Question

Apparently, my belt came off while vacumming. I had a lot of hari entwind on the roller, so cleaned off the hair.... but now I can't seem to get the belt to stay "in place". Is it supposed to move around on the brush? or be held in place? It seems to me when I try to get the hook to grab ahold of the belt, it is going tohe wrong way to grab it. Please HELP!