Quoted from cody_chunn:Best to replace it.
As mentioned, over-tight screws can cause failure.
Take a look at the switch. See under the metal arm a little button that gets pressed down into the switch body? Put a drop of alcohol on there so it runs into the body and work the switch a couple dozen times. *Sometimes* this will recover operation for a while.
I've done the alcohol "cleaning" and brought switches back to life (for a while). Some gunk can build up on the contacts in the switch and this will clean them. I would also add to repeatedly depress the switch while running alcohol through.