Ok, this one is something I find myself doing fairly regularly, and never remember exactly how to do it.

If you find yourself with a computer that is too messed up to even do a factory restore, you can use a bootable USB with windows to clean things up a bit.

• Boot up Windows Installation media
• On first screen, press SHIFT+F10 then type:
  • diskpart
  • list disk (in case your largest volume isn’t Disk 0)
  • select disk 0 (or the largest volume)
  • clean
  • exit
  • exit
• Continue. Select the unallocated partition (Only one shown) then click next, windows will create all needed partitions.
  Done.

That’s all there is to it!

If you need to create a bootable Win10 disk, I recommend RUFUS. It works quickly and effectively.