Here are my suggestions. These happen all the time.
1: Stretch the prongs on the battery fitting/slot out so that they are further out and are much more likely to touch the battery harder. You do this because the prongs may not be receiving all the power from the battery.
2: The "on" light may be out, so turn it on as you normally would and then turn the eyes off and see if a light flashes.
3: check the wires in the grip frame and make sure they aren't cut/pinched.
4: Make sure everything is plugged in on the board, sometimes the wires come loose.
5: Check and make sure the button is reaching all the way to the actual button on the board and make sure it presses it down.
Hopefully these work. If not cal dye