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Is there an intel optane drive in the m2 slot? Dell didn't sell it stock with the PS on a sata drive unless the sata drive was raid with an optane drive.  Breaking up the raid setup without separating the drives would render the data on both unreadable.

In any event, you can try formating the spare HDD in disk management. Type under windows start run:  diskmgmt.msc 

Before doing that I would disconnect the hdd from the pc and make sure it's still working fine (and that the c: drive you're seeing isn't the HDD).

This was an unusual way to install a new boot drive that you mentioned.

@r72019 @ATLGREG 

Not sure if I would call it unusual, sounds like the user cloned their drive and it boots up fine. But you're right, they probably just want to use the existing HDD as extra storage space.

In this case, use disk management and format the old HDD to treat it as storage space: https://www.lifewire.com/how-to-format-a-hard-drive-2626077

Yeah what I meant by that was an OS clone could have been done in about 5-10 minutes depending on drive size utilized but doing an image and restore (not the same as cloning) from a bootable flash drive probably took like at least an hour. An image abd restore is not necessary when you can have both drives connected simultaneously.  Then you can just clone.