I’m not sure what caused it, but all the symptoms point to firmware impairment. It’s a 500 GB Seagate Barracuda 7200.12, I think. Is there a way to repair the hard drive or to extract the data without paying data recovery clinics an exorbitant amount of money?
The hard drive is unrecognised, but it doesn’t emit any unusual noises. The disk spins up as normal.
Sounds like something I just had happen a couple weeks ago. If it is, there's a tutorial on how to try and correct the problem. The model of my Seagate HDD was different from the one shown, but after following the steps, it worked perfectly. The drive became operational and all my data was/is still intact. Though, I may have just been one of the lucky ones.