Umm... you may need to retrieve the data from a backup?
Dropping a hard drive on the floor is pretty extreme. There are two things I can think of trying, but I wouldn't hold out a lot of hope for success:
A) Put the drive into a different enclosure to see if perhaps the damage is confined to the drive enclosure or it's circuit board only (seems unlikely).
B) Some people have reported that it's possible to get data back from a dead drive by freezing it for a day and then connecting it to a computer and copying the data off it. I don't know of anyone whose done this for a drive with physical damage, though.
Does the drive make any clicking or grinding noises? Does it sound different than it did before at all?
If there's physical damage to the platters (likely if the drive makes nasty noises) then your data is probably toast.. unless you want to pay a professional to try and recover the data, which can cost hundreds of dollars.
If the drive doesn't spin up at all, the enclosure might be broken, as sminlal suggests. Try a different one or move it into your computer.
If the drive seems to spin up and isn't obviously damaged, there are various tools available to detect problems and potentially recover data from a hard drive. I've used SpinRite to successfully recover data from a dead notebook drive. You have to buy it, but it might be worth a shot if your data is worth a lot to you. (link: http://www.grc.com/sr/spinrite.htm )