Was it powered when it was dropped? Some modern drives have G sensors and will retract the heads but not all will, and it might not have been quick enough. If it was unpowered the even heads in rest position can be knocked out of where they need to be by a drop.
Why are the platters exposed to open air? While it might not necessarily have ruined it you will have made things far far harder if (read "as") dust has got in there. There is a reason most of these things are doing in either filtered or vacuum chambers.
Has the thing be disassembled further than that? Granted the usual problem there of the heads stick together does not look to have happened (to properly pull such things apart unless you want to replace them then you will often want a "comb" which is a little bit of plastic shaped like a hair brush to do just that.
Short version. If it does not appear to the usual suspects (livecds of both windows and linux) then it is most likely hosed. You can try some further things but those are usually more for dead sectors messing things up and needing to read slow or read around the dead sector.
