Later I found out what had caused the problem – a bug in the firmware running on the hard drive itself was causing the data stored on the drive to no longer be accessible as soon as the hard drive was powered on.
Seagate issued a statement about the problem, as well as a promise to resolve the issue as soon as possible with a firmware update. The company also stated they will provide data recovery services for those drives already impacted (like mine).
As you can imagine, Seagate’s support lines are swamped with calls, as I found when I tried to get through yesterday. If you believe you may have an affected Seagate drive, you can contact the Seagate support team at 1-800 SEAGATE (1-800-732-4283), or send an email email@example.com with the model number, serial number and firmware revision found on the support label on the hard drive itself.
In the meantime, as with all computer equipment, this issue serves as an important reminder to make sure that you have up to date backups of all your important documents and files. I do this by keeping a local backup on an external USB drive, as well as a secondary off-site backup through the Geek Squad Online Backup tool.