i would take off the plastic cover in front of it for access to the motor and try opening it manually with a tool. That way you can see it if is sticking or if its just motor/sensor problems. when it stops have you tried letting go of the button and pressing it again. Mine gets confused once in a while. if i hit the wrong button to close it, if it is up then i have to hit the close button twice to make up for the wrong push for some reason. (if you can follow that) Its kind of strange.
good luck