Sometimes there is a divot in the ball trough, so the ball doesn't sit in the right spot in the trough so the switch doesn't activate. But if the switch doesn't function even by hand, then that is irrelevant.
Try some of this?
If a Bad Switch is Found.
If a switch does not work, check these things:
Check the switch wiring "up stream". Switches are wired in a "daisy chain". If a switch row or column wire breaks "up stream", ALL the switches daisy chained after the wire break in that row or column will not work!
If it's a micro-switch, check the actuator arm. Make sure it's adjusted properly. Listen for the micro-switch's "click" when activating. No click usually means the switch is mis-adjusted or broken.
Check that the wires going to the switch are soldered well, and haven't fallen off.
Check the continuity (using the DMM's continuity setting) of the wire between this switch and another working switch in the same column (white wire) or row (green wire).
Check the switch to make sure it works. Use the DMM's continuity setting, and put one lead on the "common" lug (the lug to which the banded end of the diode connects) of the switch. Put the other lead on the green (normally open) switch lug. The meter should only beep when the switch is activated, and not beep when the switch is de-activated. Move the DMM's lead from the green to the white wire (normally closed) switch lug. The meter should beep when the switch is de-activiated, and NOT beep when activated.
Check the diode on the switch. Make sure the diode is connected properly, and is working