in my experience, most external drives are a standard sata drive installed into an enclosure. I would disassemble the enclosures, remove the internal drive, and test the drive separately. Odds are, the drive is dead. If that is the case, repair wouldnt be an option as HDDs are incredibly delicate on the inside, and near impossible to repair mechanical faults. You can replace the hard drives inside and keep the enclosure though, which i would suggest doing.