Unfortunately it sounds as if your hard drive/the information on the hard drive has become damaged or corrupted. If the console is showing the hard drive as being 'unformatted' then you will need to reformat it to try and fix the problem. Simply
hit Y on your controller and select "Format Hard drive", you will also need the console's serial number which can be found via "System settings" and then "System Info".
If reformatting the hard drive does not work then contact the xbox support line to see if they can send you a replacement. You can also review the troubleshooting advice here on the xbox.com support pages:
Troubleshooting hard drive issues
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