You appear to have physically broken the harddrive when you dropped it. Or at best the connection cable to it has shook loose.
If it's broken you will have to buy a new harddrive to replace it.
May I suggest if you do not know how to go about this then you take it to a little local shop for them to do and they will also test your harddrive to see if any data can be recovered. It will prob cost about £60 - £80 to repair plus the cost of a new harddrive if needed.