Windows 8.1 will not install.

Hi, Finally decided to sign up after spending the last 8 days following "how to's" on this forum. Whatever I try, I can't get Windows to install onto the desktop PC. This computer was running perfectly fine up to the 10th June 2016. It was running Windows 8.1, the exact same Windows 8.1 I'm trying to install again now, same license key, same retail CD. I had decided to set up dual boot...