How far was the drop? LNB's are pretty stout. I have seen one drop from a roof and land on concrete. The plastic casing shattered but no damage to lead housing. Took one apart to see whats inside - nothing but a circuit board; no moving parts at all. The LNB that dropped still works.

If it's a dual LNB, try swapping to the other output.

Other than that, make sure you're pointing in the right direction. Two degrees can be the diference between peek signal and 0 signal. Keep in mind that the coordinates for your zip code should be considered a starting reference point and not exact. Dish manufactures don't seem to have very tight tolerences and I've seen a few that are very close to the mark but many more that are several degrees off of the reference point.

By "old directv system" I'm guessing you mean a round dish. If it's also an old receiver that's been activated before than I don't understand why you are not getting a "you have inserted the wrong access card" message. You could have problems with the receiver instead.