The other is a USB connected HDD which I cannot access, both show in "Device Manager" as working OK.
Does the drive have any data on it? Is it formatted?
Can you see the drive in disk management ?you may need to assign a drive letter.
One is a camera which I can access from a desktop shortcut and it shows who is at the front door so I know it works OK.
I would not expect the camera to show in My computer as it is not a storage device.