OK, we are struck with this problem on another thread also concurrently. In the other case it is an internal drive put into an external casing.
Definitely we are now shooting in the dark without really knowing what exactly is causing the problem. The only thing we know is that the drive is faulty. What exactly is the fault in the drive? - we don't know.
I would suggest two explorative runs.
1. Download , install and run Minitools Partition Wizard Home edition 8.1.1
Free download Magic Partition Manager Software, partition magic alternative, free partition magic, partition magic Windows 7 and server partition software - Partition Wizard Online If it shows your drive, post a screenshot.
2. If it also does not show that 1tb drive, we shall straightaway embark on a data recovery attempt.Prepare a Lucid Puppy pendrive and check whether you can access the drive and retrieve the data in it.
Download Lucid Puppy (Ubuntu Compatible Build) version 5.2.8 ISO (132.6 MB)
Download latest Puppy Linux release
Create your bootable pen drive using Rufus v 1.4.10 (616KB)
Backup all data on your pen drive before using Rufus since all that will be lost when Rufus formats it.
With your pendrive connected, run Rufus, check your correct pen drive is selected.
In "Create a bootable disk using" select ISO Image with the dropdown arrow. (Leave everything else to dlefault.)
Cick on the Disk icon next to it and select the Lucid Puppy ISO.
Click on Start and allow Rufus to complete writing the ISO to the pendrive.
Close Rufus.
Now connect your problem external drive and another external drive on which you want to copy the recovered files and then reboot your computer.
Use the one-time boot menu and boot from the USB pendrive.
Wait for Lucid Puppy to load and you will be in the Lucid Puppy desktop.
On how to use Lucid Puppy see
Lucid Puppy way to recover files from a non-bootable computer ( Read only what is under the topic
Recovering files from the non-bootable Internal Drive: - In your case it will be your inaccessible 1TB internal drive.
Please note that all partitions will appear as drives and you should be able to recognise them by their size.
If you can successfully recover all data, then you may try to repair your drive with File Check in MiniTools Partition Wizard or format that drive, or run the manufacturer's diagnostics/repair utility
I have given priority to the data recovery attempt.