|Assuming it's not a configuration issue, it sounds like you have failed hardware. |
Not a whole lot you can do with a hard drive that failed in that fashion. First thing to do would be to move the drive to an external enclosure, and see if you can access the files on the drive. If so, return the drive to the original drive, and see if reseating the connection fixes the issue. If not, the motherboard or SATA cable in the PC are bad. Could also be an indication of a failing power supply.
If you were unable to see the drive in the enclosure, odds of recovery drop dramatically. Since the drive disappeared, you're probably dealing with a failed circuit board. If that's the case, your best bet would be to take it to a professional data recovery service. They have the tools and parts required to replace the PCB, and access the data on the drive. Expect to pay thousands of dollars.
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