Thank you all for the replies and links!
As far as I know, Seagate sells this kind of drives to end consumers as well, not to OEM's only, e.g. Dell. Thus, I reckon there should be a way to reset, so to speak, the drive.
I am sorry I did not put all the details in the first message initially. I have been looking into this issue for about 3 months already, when I have a free time, and it seems I start to forget bits of what I have tried. Please do not suspect me in anything bad. It just keeps me curious and I do not want to waste an otherwise healthy fast HDD.
If I find something interesting, I will post here. Meanwhile, I will try my luck with hddguru