I tried two different HDD and the problem was the same for both. Any way to test the dock, it is brand new? I do not have another cable so???
I've noticed that the newer TT docks are more difficult to get the HDD seated in them properly, but I don't think that's your problem. If the HDD isn't seated correctly, it won't work at all. In your case, it sounds like it could be the HDD, the cable (don't think it's that or you would have had a problem right away), or the dock itself. As P Smith
said, you really should hook that HDD up to a computer and see what you get. Or do it my way, buy a new HDD and see if that clears up the problem.
Reading what I just posted and knowing what you've done so far, I'd be looking at the HDD. You seem to be doing a good job of troubleshooting.