Formatting a drive is the process of deleting all information contained on the volume. A drive is "unformattable" when it is the active drive containing the operating system files, as modern operating systems will not provide you with the option to self-terminate while active. Circumvent these restrictions and reenable the ability to format your volume by accomplishing the procedure through DOS.
Insert the DOS boot disk into your optical disc drive. Click the "Start" button and select "Restart."
Press any key when prompted to boot into DOS.
Type "Format x:" and replace "x" with the letter of the hard drive you wish to format.
Press "Enter" and "Y" to confirm, formatting the hard drive.
Formatting a hard drive removes all information from the drive, including the operating system. Create backups of all important files and programs before formatting the hard drive. If you wish to continue using the computer, install a new operating system to the hard drive.