The suggested tapping is likely to get the tumblers to settle in to the slots on the key. Since the light tapping has not worked yet, the tumblers might be seized in the cylinders. I'd suggest spraying some penetrating spray in to the key slot first, then insert and remove the key several times. Then try lightly tapping the head of the key while turning. If you get the cylinder to move, be prepared to replace the key cylinder right away. You don't want to get it started only to realize you're going to have to shut the car off again until you get a new key cylinder.
-Rod