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1. Try to connect this HDD to another computer and see if it is detected
2. Try to reseat the cable or even try another cable connecting your HDD to notebook
3. Connect this HDD to a different USB port on your notebook.
4. Does this HDD appear in BIOS
5. Does this HDD appear in Disk Management (Right Click on Computer >> Manage >> Disk Management) - if it appears here, it should have a drive letter assigned (like D: or E: etc). If there's no letter assigned, you need to assign one.
Hope something works out for you - Good luck and A Happy New Year!!!