The Verbatim external harddrive may be damaged beyond warranting repairing, either from you, or a professional computer shop.
Allow me to explain the construction of an external Harddrive, plus the Harddrive located inside the case, and what may have resulted from the fall.
Basic construction of an external Harddrive, (IDE or SATA)
1) Plastic external case. Also referred to as an External Enclosure. Usually comes apart in two halves.
2) Small circuit board located inside, with an interface that the Harddrive plugs into.
3) Harddrive. IDE or SATA. Can be a 2.5 laptop harddrive, or a 3.5 desktop harddrive that is used.
[A laptop harddrive is 2-1/2 inches across in width. A desktop harddrive 3-1/2 inches.
If you have the Verbatim Leather Wallet 640 External HarDDrive it has a 2.5 inch laptop harddrive inside. The harddrive is a SATA unit.http://en.wikipedia.org/wiki/SATA
View of an average 2.5 inch (Laptop) 640GigaByte harddrive,http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=5260951&CatId=2681
(The harddrive inside the Verbatim external harddrive enclosure, may not have a clear see-through cover to observe the internal workings )
The back end of the harddrive has contact pins. These pins line up with an interface.
The interface is a block with matching socket holes for the contact pins.
(Or more than one interface may be used)
The interface 'block' may be attached directly to the circuit board, that is inside the Verbatim external enclosure (Case), or may be attached to cables (Wires) that are then attached to the circuit board.
A) Point; The circuit board may have a crack. (Copper circuit trace is torn, or more than one)
[Circuit Board. Also known as PCB. Printed Circuit Board. Crude description of construction is a laminated board with very thin copper wires on it.
This information details out the construction of PCB's,http://en.wikipedia.org/wiki/Printed_circuit_board
If cracked the circuit board MAY be repaired. Finding the open circuit, (Broken circuit trace. 'Copper wire'), may be VERY tough.
The circuit board may be replaced. From the factory will cost $$$$, and perhaps the loss of information that is on the harddrive.
To my knowledge the needed circuit board is not sold to the average consumer. This would mean obtaining another like Verbatim 640GB external harddrive, and using it's circuit board.
More feasible; The harddrive would be removed, an inexpensive external enclosure procured, the harddrive then installed inside, then the USB cable from the external enclosure is attached to a working computer, and personal information is then copied off.
(Hope you're not an English teacher, and reading the above, lol!)
B) Basic construction of a Harddrive:
1) Inside the hollow empty metal shell of the Harddrive are two motors.
The Spindle motor, and the Actuator motor.
There are 3 to 6 Platters inside the Harddrive. (Perhaps more in today's Harddrive's)
The Platters resemble CD or DVD disks, and are usually composed of metal or glass.
The Spindle motor drives the Platters.
EACH Platter has a magnetic media applied to it's top surface, and bottom surface.
The magnetic media is arranged in a pattern of 0's and 1's.
1 being ON, 0 being OFF.
(The magnetic media is arranged in Sectors and Tracks much like a CD or DVD disk)
The Read/Write Head arranges the magnetic media. The Write portion of the Read/Write Head does this. (The Read portion does as it implies. It reads the information on the Platter)
There is a Read/Write Head on the Top, and on the bottom surface for EVERY Platter.
When the computer is off the Read/Write Head is in a parked position, and away from the Platter.
When the computer is on, the Read/Write Head is 'hovering' right above the surface of the Platter.
The distance of the Read/Write Head to the surface of the Platter is VERY CLOSE.
The Read/Write Head is attached to an Actuator Arm. This arm swings the Read/Write Head back, and forth across the surface of the Platter.
(When operating, the Actuator Arm can swing the Read/Write Head back, and forth across the Platter at Hundreds of Times a Second!)
Point; If the Verbatim 640GB was plugged into your computer with the computer on, and then dropped, one or more Read/Write Heads could have crashed into a Platter. (Or Platters)
This would result in wiping off some of the magnetic media, and may have rendered the Harddrive useless.
I know. I'm just a ray of sunshine.
I would suggest removing the harddrive out of the Verbatim's case, and installing it into a matching external enclosure, to try to remove any needed data.
OR take it to a professional service that recovers information from damaged harddrives.
An external enclosure is cheap,http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=1086960&CatId=2781
This is to just check out the harddrive, and see if it's still functional.
For questions, or clarification to what I have stated please post in a Comment.