It may actually be powering on, but the screen is dead since the fall. Alternatively, it may be a broken connection between the battery and the phone itself. Try plugging it in without a battery inserted, and powering it on.
If it does power up, then you know it's the latter.
Either way though, the device would need to be repaired. Take it to a cell phone store and ask them to take a look at it. They could give you an estimate on what it would cost to repair.