The drive has been damaged when it fell off, most likely the read/write heads have crashed into the platters which contain your data. The drive is now unusable.
The only way to rescue any data which hasn't been damaged is to send the drive to a data recovery company, but that is very expensive, and they won't be able rescue all the data anyway because some of it has already been destroyed by the mechanical shock when it dropped.
You should never save important data on only one drive. It should be saved on at least two separate drives, because even if the drive is never dropped, it will still fail eventually just by the wear-and-tear of using it.
Is it broken or physically damaged?
The falling thing usually can do some damage to the hard drive in two ways: physical damage and logical damage. The logical damage still can be fixed by formatting. However, the physical damage is not so hopeful.
Therefore, in order to access your data again, you should try a hard drive recovery freeware that has helped me recover my videos, music, photos and files from a corrupted drive. You should have a try!
1. Stop writing anything new on the same drive to avoid original data overwritten by new data, which can make your data gone permanently.
2. Save your recovered files on a different storage device in case of recovery failure.
3. Always back up you data in the future.
If the recovery process doesn’t work, you should take it to a specialist or data recovery company for help as soon as possible.