I had a similar Issue with 4x 4GB on the RIVE board a while back. I simply re-seated the CPU as not all pins were making contact.
This has since solved my issue. Give it a try. Hope this helps..
Case: Coolermaster HAF 932 | MB: Rampage IV Extreme | CPU: Intel Core I7 3930k @ 4.8Ghz | RAM: 16GB G.Skill Ripjaws 2133 | GPU: 2x Asus GTX670 DCII OC 2GB | HDDs: Samsung EVO 250GB + Crucial M4 128GB + Intel X25-M 80GB + 3x WD 1TB | ODD: Asus DRW-24B1LT | PSU: Seasonic X -750W | Cooling: H100 with SP120 Fans push/pull