It sounds to me like your button may be stuck. Check carefully for lint/dirt/grime in and around the button. With machine off, clean your buttons per manufacturer's suggestions for cleaning materials.
It won't hurt the machine to take the cover off..(just tape each screw near each hole as you go), so you can put it back together with the right screws in the right place..then check your reverse button to see if it's jammed with lint or dirt. While you have it open, take a very soft brush and clean lint from anywhere that you see it.