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#11
You should be booting the computer from a Windows 10 installation USB flash drive. You can use the Media Creation Tool and let it make a USB flash drive for you:
Download Windows 10
If you have the Windows 10 ISO file already saved you can make your own. Format the USB flash drive as FAT32, mark the FAT32 partition on the flash drive active, mount the Windows 10 ISO file, copy all the files and folders from the mounted ISO file to the USB flash drive.
Boot the computer from the Windows 10 USB flash drive. When you get the first screen, press shift + F10 to open a command prompt. Run:
diskpart
list disk
select disk # <put the number of the hard drive in the computer in place of #. It is probably going to be select disk 0
clean <this completely erases the selected disk
exit
bootrec /fixmbr
exit
Then continue with the install. If it asks you for a product key, click the link for "I don't have a product key". Select the custom install option. Highlight the unallocated space on the hard drive and click next to let Windows set up the drive and install Windows. When the computer reboots, if you go back into the first install screen from the USB flash drive, just pull the flash drive out and reboot the computer.