Hi David,
Is it the 447Gb drive you are installing Windows onto?
if so, that drive is not GPT, use these steps:
At the very start of the Installation Process, press Shift + F10, or Shift + Fn + F10 to open Command Prompt
Run this command and hit Enter:
diskpart
Run this command and hit Enter:
list disk
Run this command and hit Enter:
select disk 0
Run this command and hit Enter:
clean
Run this command and hit Enter:
convert gpt
Then close Command Prompt and begin the installation.