Windows cannot format the system partition on this disk

[Rapson_27]

i currently have a 1tb hard drive and a 64gb ssd. the ssd is only being used and the hard drive isnt. when i go onto disk management and try to format the drive. an error message comes up saying that "Windows cannot format the system partition on this disk". please can someone help me to sort this out. i am also currently using windows 10 pro

 

[hang-the-9]

Need full system specs and how Windows was installed on the system. Did you build the system? If you did, was the 1 TB drive ever used? Need full details about the setup. If you have a system partition on that disk that means that Windows has installed system files on the disk, which means it should be formatted already. Does the system boot if you remove that drive?