Had it happen to me and I found out there's a few ways this could happen.
1. You got hacked. Some jerk decided to hack into your HDD and just destroy it. Not too sure about the specifics but it isn't an automated thing. You would have to royally piss someone off to make them put the effort in to do this.
2. The HD was on an angle for an extended amount of time. This ended up being my problem. It throws off the calibration and the system can't recognize it. It can be fixed but I didn't bother.
3. Vibration for an extended amount of time. If it wasn't mounted right it will shake. Shake long enough and it does permanent physical dmg
4. Some kind of hardware malfunction. If it took a quick hit or fell could have messed with some of the inner workings. When the tech explained it to me it sounded much more scientific then that.
I wouldn't know if it's exactly the problem I had. But it was the same thing for me. Hope this helps. It pretty much meant for me buy a new one. Maybe someone else has a more helpful solution