I was installing Windows 10 onto a brand new SSD the other day and it was stuck at the "Copying Windows Files"
Many posts on the internet were talking about waiting or checking disk or trying a DVD installation disk rather than a USB installtion stick. None of these seemed right to me. I decided to check the BIOS settings and this is where I found the solution.
Given that I have done this hundreds of times before I was confused as to what was confusing the problem. I found the problem to be caused by a security setting in the BIOS. As soon as I reset the security keys Windows 10 reinstalled fine. Under Key Management I restored factory defaults.