Welcome to the community, @Tom!
Unfortunately, it sounds like you have damaged the external HDD with the drop.
Physically corrupted drives are very dangerous to tamper with, especially if you are trying to retrieve your files. Just like @Ralston18 mentioned, it's probably a good idea to check the health and SMART status of your external HDD using
an HDD-specific diagnostic utility . If you are unable to get the drive detected, you should probably consider contacting a professional data recovery company as they would be your best bet on getting your data back. If you decide to do data retrieving attempts by yourself, you should be aware that it could potentially do more harm than good and it'll be at your own risk. Are you able to see the drive in
Disk Management?
Keep us posted with the HDD diagnostic results.
Good luck!
SuperSoph_WD