How can I reformat a used hard drive which is not accessible in Windows?
You can format it with bootable windows disk or linux disk or partition manager disk.If you don’t have any bootable disk then you need to purchase it then you can simple boot computer with bootable disk like if you have bootable disk then insert that disk into cd/dvd rom drive then when you power up the computer press F1 or F2 or del key to enter in bios then go to boot menu and set first boot device as cd/dvd rom then save settings and exit then it will boot with disk then select graphical user interface then on disk partition screen delete all partition or format then you can use it again.
You can attach the hard drive to another Operating System like Linux, MAC and see if you can format the the HDD using their disk utilities. You can also download an ISO and burn to Disc programs like GParted. Boot from the live disk, then use Gparted to reformat the hard drive. After doing this I suggest using the “Disk Check” option to ensure the HDD appears to be good and usable.
