Welcome to Tom's Hardware, @hami01!
Is this external HDD a brand new drive or do you have data stored on it already?
I'd strongly recommend you check if the HDD is listed in
Disk Management in Windows. If it's a brand new drive, you will need to
Initialize it and then
Partition & Format it through there in order to make its capacity available through My Computer/This PC (File Explorer).
Keep in mind that these steps are recommended only if you don't have any data on the drive. Initializing and formatting the HDD would wipe out the drive and erase all its contents!
If the drive has data on it and you somehow are not able to access it, then I'd suggest you swap the USB cable and the port where the external is connecting to your computer. If you have access to another PC/laptop, you should also check how it would get recognized there.
Let me know how it goes and keep me posted with the troubleshooting details!
SuperSoph_WD