The advice below is based on just what info you have given in the question and that the USB controller sees a drive and so I’m assuming the controller is working.
1) Turn the drive off right now. You have a spinning platter hard drive that was dropped while it was running, you most likely have had a head crash ( if the head is not “parked” when it was dropped the head will hit the surface of the spinning platter and damage the head and the surface of the disk).
2) IF it is a head crash and I think it is, software will not fix this type of failure but if you want to follow the software path I have had very good luck with Spinrite
http://www.grc.com/sr/spinrite.htm but you will need to connect the drive internally and not on a USB adapter.
3) You will never have those 3 years again. If it were me I would just not risk anymore damage to the drive and send it to Drive Savers
http://software.bigbigsoft.com/data-recovery-mac You are going to pay through the nose but they should be able to get the data back.
4) Storage is cheap, if you don’t have it saved in two places you don’t have a backup. I have four copies of all my wedding photos. DVDs are very cheap too, send copies to the in-laws every year.
5) Hard drives fail, period.
6) Good luck.