How to recover data from corrupted external hard disk

If it is those sealed HDD's you have no way of doing data recovery WITHOUT voiding the warranty.

If the hard drive enclosure can be opened, take the drive inside & try connecting it to a PC.

If it doesn't work (and your data is more precious than the warranty), give it to a professional data recovery center. If they can, they will recover your data for you.

Prying open a Sealed HDD is an option, but remember IT VOIDS THE WARRANTY.

Does the Disk management show it as a healthy RAW partition? If yes, you may try to use R-Undelete. Its on-line help will show how to get your files back: Recover Lost Files from Deleted/Corrupted Logical Disks/Partitions.
R-Undelete is a pay program but it allows you to estimate whether you can recover your files before buying it.

How does HD Sentinel detect your drive?
http://www.hdsentinel.com/

How does Microsoft's UVCView utility see the external drive?
http://www.users.on.net/~fzabkar/USB_IDs/UVCView.x86.ex...

UVCView communicates with the USB-SATA bridge board inside the enclosure, whereas HD Sentinel tries to communicate with the HDD behind the bridge.