I would make sure that you didn't unseat the PIC or the 485 chip. You may have a bent pin on one of those IC's that was just making a connection before the board was jarred causing the component to move. The easiest way to tell is to remove the chips and check the pins. If they went in straight, then they should come out the same way. If you remove a chip and it has a bent pin, that was your problem. Just straighten the pin and put the chip back into its socket and be carefull. They have some tolerance for bending the pins but they will only tolerate so much before they will break off. If you reflashed the PIC and it took, I would look more at the 485 chip. The only component on that board that can be really sensitive to shock is the crystal and even there, that board is so light that I really don't see much of a significant shock just dropping it.