If that PC is still under warranty, then take it back and have it looked at.

If not, then open the case and check to see if the cable connector has worked loose on the drive (or the power connector).

If all connectors are firmly attached, and the drive stil doesn't detect despite being set to Auto, then I'd suspect the drive is dead! It's not unknown for drives to fail like this. Was slowness the only reason for formatting? Were you getting any errors previously?