It won't let me delete all the folders from the drive an idk why
You have to take out the HDD, inset it into another computer, and format the drive. I had to the do the same thing once because Lenovo DRM was in it. Afterwards you can do what you wish the newly formatted HDD.
Boot to a USB with FreeDOS and command line format the drive.
If you were intending on just removing Windows and keeping everything else, either connect it to another machine or boot a live o/s from a USB
Otherwise just format the whole drive
You could use http://www.sysresccd.org on a usb to reformat the partition, or on a CD if you still use those.