How do I recover data from my presumably dead hard disk

Sounds like you've been bitten by the BSY bug (the drive event log location has been set to an invalid location by an off by one error in the firmware). This contains a reference to your model being affected. At one time, you could send the drive into Seagate and they'd revive it by updating the firmware, you'd end up paying only for shipping. Hopefully they're still doing that. If not, you can do it yourself (another link). If you've got more of theses drives, get the firmware updated while they're still operational.

Update

Here are some additional links. This one seems to be a good general introduction that discusses the cabling / voltage requirements for communicating with the drive. This one has more details / discussion.

If your device is not being recognized by the system, that might indicate a bad controller. That's good, because it means your data is likely still safe on the disks themselves. But it's also bad, because you'll need to use a data recovery firm that can replace the controller in a clean room environment. But at least there is a relatively high chance of their success.