Sorry if this has been posted before, but I wanted to share my experience because I nearly gave up before solving my problem.
Tonight my hard drive "died." In the middle of playing back a recording, everything just stopped, and Tablo showed "No Hard Drive Detected." After the usual troubleshooting steps (Tablo Reset, plug Hard drive into my computer then plug back into Tablo, etc.), no luck. However, the hard drive light came on, so I knew it wasn't hopeless.
I noticed that even when plugged into my computer, the external hard drive did not show up in Windows Explorer. This was unusual. However, the drive DID appear in the Windows Device Manager, so I knew the drive was alive, but crippled.
After exhausting all the steps in the Seagate external drive troubleshooter, it suggested repartitioning the drive, but gave no guidance on how to do that.
I downloaded Paragon Partition Manager (free) and deleted and recreated the partition.
WARNING: If you use this program, make sure you are partitioning your external USB drive, NOT your computer's hard drive. Oh man...
Even after recreating the partition, the drive would not show up in Windows Explorer, but it now showed up in Windows Disk Management. Progress!
In there, I right-clicked on the drive, and was able to assign it a Drive letter ("Add drive letter" option). WALLAH! Now it was showing up in Windows.
In Windows, I formatted the drive with FAT32 file system.
Reconnected to Tablo, and now it recognized the drive, and asked me to format it. After Tablo formatting, I'm back in business. Yes, all my recordings are gone, but I consider it a small price to pay after a couple hours of thinking for sure I was going to have to buy a new hard drive.
I have no idea why this happened after a year of pretty reliable use from the drive, but I'm glad I figured out the fix. Hope this helps somebody who thinks their hard drive is dead.
PS The above references a Seagate BackupPlus 1TB drive.