I have a laptop with Windows 10 on the single drive. Because I was lending it to a friend, I needed to clear the drive so they could install their software. I backed up an image of the drive, and was ready to reformat it. Clearly, I couldn’t do that from within Windows.
The first step was to make sure I had a Windows repair disk. I did, on a USB complete with system files.
The next step was to change the boot sequence so that it tried the USB device before the hard disk.
Then it was just a matter of restarting the system.
Once the USB had loaded the repair/recovery screen, I chose Troubleshooting from the menu:
From the Troubleshoot menu I selected Advanced Options, followed by Command Prompt.
I entered the format command: format C: /fs:NTFS
(NOTE: If the C: drive has a volume name, e.g. OS, it will prompt for this.)
The reformat didn’t take long, as it resets the indexes rather than wiping the drive. In other words, using the right tool, the data is recoverable, but I knew that wasn’t going to happen.