Did you try to disconnect the hard drive and reconnect it?
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=== Update (06/03/2020) ===
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My wife's ipod classic 160gb hard drive stopped working so I am completely rebuilding it with a new black faceplate and a red turn wheel. A new thick back case that is etched 256gb. It has a new screen, battery and hold/power button. I also got rid of the hard drive and bought the iflash and 2 128gb sd cards. If I need it I can even get a new motherboard. She is happy, she loves it and she loves music. It was one of the first gifts I gave her.