If the red knob on the back of the Time Timer MAX isn't properly set in its groove, this will sometimes effect the movement of the disk. If the red disk still does not move after adjusting the red knob on the back of the timer, try removing the center knob on the front of the timer (top part only). Then use a screwdriver to gently tighten the center screw under the knob in the middle of the timer. This process ensures the disk is securely attached. Next, replace the knob cap and make sure the clear lens is completely snapped down.