How can I recover a "lost" HDD?

Regardless of its state, if the HDD is electrically sound, the BIOS POST should report it. If your BIOS does not report the HDD, then it could be mobo, bricked green board, or the cables have come loose.

For openers then, disconnect and then reconnect both drive and PSU cables (both ends). If that does not work, swap out the PSU cable to an unused cable (or temporarily disconnect one from an ODD). Also, swap out the drive cable with a spare or one from another component.

Even though you did not change them, double-check to make sure your BIOS settings enable and point to the drive.

Also, try a different port on the mobo for the drive cable.

Monk

BIOS/Hardware level:

Is this an eSATA cable or USB connection? (I'm assuming eSATA, but if USB then that's another ball of wax.) *Ok in your specs I see eSATA for your external WD 1TB.*
What type of enclosure is it in and what is powering it? Sometimes enclosures have data/partition limitations.
What mode AHCI or IDE (if SATA)?
Does your MOBO have the latest bios? Sometimes 1TB aren't detected correctly by certain bios.
Does your 1TB have the latest firmware? (WD have these problems)
(sorry for all the questions, but multitudes of things can affect external eSATA/USB)

Is it possible to temporary switch some drives, try the 1TB in your case and another on the eSATA or USB? This would help immensely in narrowing down the culprit.

Is the connection cable SATA, or hybrid (SATA/eSATA)?
A vanilla SATA cable can cause this error.
Always try to use short cables and out a port from the rear of the case. Long cables and using a front port ( basically another long cable) can also cause drives to fail.(this goes for both SATA & USB)

OS level:
(since bios doesn't see it, probably won't work, but still good info to know.)

What controller is your eSATA or USB?
Is the controller enabled and also have the latest driver? Is it a jmicron controller (SATA)?

You can also try this:
Right click on Computer in start menu
Click Manage
Click Disk Management
Click Action
Click Rescan Disks

Yes I'm taking a shotgun approach...lol, but every single one of these can cause eSATA/USB failure. Sort of difficult trying to diagnose on this end, but with Hmonk and the rest of the crew here, something will come to light for you.

First off, an I/O (input/output) failure generally means that the computer and a device are not communicating. Why? Could be a HW issue, e.g., electrical/mechanical or a SW issue, e.g., drivers.

In my computing history, most I/O errors that I have received were HW issues, most often either faulty connections or faulty components.

If you are satisfied that your connections are sound, one thing you could try is Kill Disk which you can get for free. (the "pro" version is also free: all you have to do is complete a user survey). What it is able to do, if the HDD/mobo/etc. are otherwise sound, is to access and wipe a HDD of all of its data (not HDD firmware, however). The object is to clean the HDD of any conflicts that might prevent the Windows OS (not BIOS) from being able to access or initialize the HDD due to those conflicts. If that fails, then I would conclude that an electrical/mechanical defect exists within the HDD itself, i.e., it is bricked.

Monk