|Hopefully you have all of that data on another drive as well.|
If it is under warranty then sending it back is probably you answer (If you need to recover your data then skip this for now since they might send you a replacement drive).
If you need to recover your data then I would open the external case, remove the drive, and plug it in as a secondary internal drive on a desktop computer and if it works, copy over your files to another drive.
If the drive itself is good then you can put the drive into a new external case, look for a repairable problem with the old case, or reassemble and return it for repair (if any warranty is not now voided).
If the drive does not work as an internal drive, check in Disk Manager if the drive shows up there and report back what it shows about the drive for more advice.
You have to be a little bit crazy to keep you from going insane.