If the screen is still working perfectly, it's a harder fix than you or I could do. If the screen is even discolored or different in any way after you dropped it, the problem would most likely is the connector from mainboard (the part with the keypad) to the flip screen where the speaker is.
If the screen is different, I would take the phone apart and reconnect the ribbon cable firmly.
That's my only guess:S Wish I could be more helpful.
good luck
Patrick Sewell, January 2008