If I could make the cd bootable with the dos commands, I could just format C:.
On a Windows 7 PC you create a Windows Repair CD via the Control Panel / Backup and Restore.
On a Windows 10 PC you run the command RecoveryDrive.exe to create a bootable flash disk. Do NOT copy the system files.
You can use either to boot into repair mode, then open a Command Prompt and clean your disk. Diskpart.exe would be much better than format.com.