Gigabyte 970A-UD3P Motherboard, AMD8320, 8Gb Corsair vengence 1666mhz, having problems installing operating system, when I boot pc im told that no bootable devices can be found. This is my first build and I need an idiot proof step by step guide on setting Bios correctly so as I can put windows 7 disc in optical drive and install. Pleas help, many thx.