In order to save some information on the drive you can attempt to connect it and access the partition containing your storage using a partition recovery program such as
Partition Recovery.
Also in the next step there is a chance that the Windows.Old files will be left containing certain key information before the DISKpart clean stage.
If the hard drive itself is so corrupt that the computer wont boot even when its not selected as boot priority or you can not get it to open period while connected.
The best scenario for this would be to connect the Hard drive alone, and insert a OS disk for the harddrive, then boot from disk, this will allow you to reformat and rewrite the disk with a new OS on it, afterwards I would highly recommenced cleaning the drive of anything left on it.
after that I would use Disk Part to clean and partition the drive for further use.
Afterwards you should have a good, usable 1tb external HDD completely reformatted.