That doesn't seem good as there's no unallocated space.
Go ahead and try the drive with a different computer as well, just to see if the same thing happens. Then you should download the HDD manufacturer's diagnostic tool and test the drive for errors. Also make sure that the product model on the label matches the one that you'll see on the tool.
You could also perform a low level format (make sure that you don't have any valuable data on it because it will be deleted), to see if the drive is recognized with its full capacity after that. Here's how to do it:
1. Open CMD (Command Prompt) as admin.
2. Type in
diskpart and press "enter"
3. Type
list disk and press "enter"
3. Type
select disk X and press "enter". Where "X" is the number of the disk you wish to format so make sure that you've selected the proper one so that you don't delete the data from one of your other drives. E.g. if the external drive is disk 2 you should type "select disk 2". You'll know which one it is by its size. Once you've pressed enter you should get a message similar to "Disk 2 is now the selected disk".
4. Type
clean all and press "enter". Now, this process will take a lot of hours if this is truly a 4TB drive so even if it seems like it's no doing anything, don't stop the computer or disconnect the drive or close the window until you see the following message "Diskpart succeeded in cleaning the disk".
After you've done all that you should open Disk Management again and initialize, partition and format the drive. Check those links on how to do that:
How to initialize or write a signature to a secondary hard drive or Solid State drive in Windows &
How to partition and format a drive on Windows and Mac OSX.
Please let me know if you can see the full capacity of the drive after all of that.
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