I'm trying to install Windows 8.1 (which I got via Dreamspark, so no optical media) onto a new build with a p8z77 mobo and a Barracuda hard drive. The system boots into BIOS fine, but it simply doesn't detect the bootable USB media at all. I've tried plugging it into the case's USB ports as well as one of the ones on the mobo itself, but to no avail. What else can I try?