There's a well-known saying in computing circles, which is that "data only exists when it's in more than two places".
Amos Gunner - when you plug it in to the computer, does it make any noises at all?
Imagine a vinyl record player - there's a rotating disc with a "read" head that tracks across the surface of the disc. Minaturise that a few dozen times and make it work on magnetism and that's a rough idea of what a hard drive is. The platters (the vinyl record in the comparison above) are incredibly thin and fragile - from memory I think they are many times thinner than a human hair. When you drop or knock a hard drive, the risk is that you make the read arm "jump" and bash into the platter. If that happens, it could damage the platter so whenever the read head passes over that point it skips and further damages the platter. Eventually the platter will be unreadable - it can be repaired at
huge expense but usually there's no point. This is called a "head crash" ('cos the read head is literally crashing into the platter). The most usual symptom is a rhythmic ticking or clicking noise (the "click of death"). If you ever hear this, BACK UP YOUR FILES NOW! Of course, you've all been good and taken regular back ups, right?
Anyway, back to the point - if it's clicking you are probably screwed, but there are some things you can try, none of which I will recommend here as I've never tried them myself and they probably don't work. Just google "click of death" and go nuts with sticking it in the freezer and other improbable fixes.
If it is completely silent then it might be as simple as the USB connector or power cable being broken. Again, a drive enclosure will be useful to test this. Inside the plastic case of the drive will be the hard drive itself, usually in a self-contained metal case. Remove this from the plastic shell, plug it into the enclosure, plug that into your computer, and see if it works.