You can't. Without a disk image, actual installation media or a functional operating system, that backup is worthless. If you know the product key, and maybe even if you don't (Most Windows 8.1 systems will automatically activate if they were previously activated to your BIOS ID string with a digital entitlement.). You can download an installation ISO for either disk or usb from here to install from. If you do know the product key, that's helpful, if it's located on a sticker on your unit or elsewhere is recorded, but I'd try this first to see if perhaps it activates automatically which there's a good chance it will if it was a licensed copy that was previously activated...