I know it's seated properly and it's supposed to be compatible RAM.
Rather than buy new RAM - I wanted to flash the bios with the latest version. With this motherboard you can do it - without any RAM, CPU or GPU! The feature is called Flashback. (It will also work with all these components plugged in so don't pull them out unnecessarily)
Download your motherboard BIOS rom file from ASUS website.
Place it onto a USB flash drive. Ensure the Flash drive is formatted to the FAT filesystem and not NTFS etc.
Make sure it's the only file on the USB drive (a precaution)
The ROM file needs to be named perfectly for your motherboard model. In my case it's P9X79PRO.ROM. To find your correct filename, you can look at the root of your installation DVD where you will find a correctly named factory default ROM file.
Make sure your computer is plugged in with power to the motherbaord but the computer itself is switched off (no fans will be spinning etc).
To flash your bios simply plug your USB drive into the white port (White on mine anyway) of the motherboard and push the little bios buton next to it.
The light on the USB and the light on the button should flash until the process is complete.
Go make a coffee/tea it's going to take 5 minutes or so.
Once the flashing has stopped try booting your system.