Why does the up button on my acer c720 keep popping off?

The buttons on the keyboards sometimes have little tabs on them that keep them in place on the computer, if one of the little tabs has broken, then it would not stay on the keyboard. Look at the bottom of the button, usually its a small round area with a few small tabs or a small hinge like device. If either one is broke or missing, then the key won't stay on by its self. You can more than likely replace just that one key, or the entire keyboard.

Usually this problem happen, when there is carbon in your key or your key is automatically touching the socket box. so in this situation you need to go open your keyboard and then clean it properly. it will start working fine.

clean your keyboard