Yes, that's what I want to do. I want the delete everything on the hard disk where I'm running windows from. So I would need to reistall windows with a cd or a usb and format the HD?
But you can't tell Windows to format the actual drive it is running from.
That's like asking you to cut your own head off. You can't. You can start the process, but you will die before it is complete.
You'd have to boot from something else to format this drive.
Ok then find out what make your HD is go to their website dl software convert to osb drive or cd and blank away. You will have a like new HD. Now if you still want there to be the OS on it and it is win 7-10 go to control panel look up recovery and start the process there. It will remove everything and reinstall windows( but to be honest I'm not 100% it will work with win 7).