If the drive is a recent purchase you should contact Seagate to determine if the drive is eligible for warranty replacement.  If the drive was delivered with your computer, and your computer warranty is still in effect, you must contact Dell Technical Support.  I'm afraid there is no way to make the drive operational if the manufacturer's diagnostics cannot find the drive.

You can try re-seating the data and power connectors to the drive, but if that does not work I'm afraid replacement is the only option.