The hard drive is either defective or the connector is not completely connected.
First remove the battery:
https://support.lenovo.com/nz/en/solutions/migr-68269
and then the hard drive:
https://support.lenovo.com/nz/en/solutions/pd010986-hard-drive-removal-and-installation-thinkpad-x60-tablet-x61-tablet
and YouTube video:
https://www.youtube.com/watch?v=QSjNHUeM9J8
Before replacing reconnect and see if that works. If still not detected then replace.