I was having problems with the foot pedal on my Aqua Magic and a friend told me to just replace the whole toilet and be done with it. I dismissed his nonsense but after several unrelated repairs (cable, water valve, seal(s), and ball valve) it works like new but I wish I had just taken his advice and replaced it.
It could just be a broken spring or it became detached but if not and your toilet is ~10 years old, you might want to think about replacing it....and be done with it.