Use any Windows 7 or 8 or 10 startup disk. When you're asked what hard drive to install to, press Shift+F10 and a Command Prompt window will appear.
Enter the following commands:
DISKPART
LIST DISK
SELECT DISK #
(Where # is the number you saw in the previous step.)
CLEAN
CONVERT MBR
CREATE PARTITION PRIMARY SIZE=50000
(The size is in MB, so enter the amount that you want to use for your system partition.)
FORMAT FS NTFS LABEL "SYSTEM" QUICK
