Hi, I'm Carl and I will be assisting you today with your Nikon Camera issue. I fix quite a few Auto Focus issues at my repair store with mostly Nikon and Canon and most of them due to being dropped. I know people hate the run around and lack of confidence in their technician so I'll try to be as straight forward but honest about this. Having an auto focus issue after a drop cannot be fixed by pressing buttons and changing settings. It was dropped and it was dropped on the lens which is now unaligned from the factory settings. The precision of a Lens is so critical that even a grain a sand can render the Auto Focus useless. The good thing is that you won' have to spend $500 on a new camera but you will need to spend around $200 to have it fixed from Nikon. It should be cheaper though. What they will do when they receive is COMPLETELY take the Camera apart and if it's not severe, repair the lens, then reassemble it. Worst case scenario, they will have to replace the lens assembly then reassemble it.
So even though it's not a quick fix, you will be saving close to $300 by getting it fixed than you would be buying a new one.
If you need any clarification or additional help, please feel free to ask me.