failed initialized

Hi ! When i installed both of my new 2x8 RAM 2666Mhz my PC wont start. Then i tried with one of my new 8GB and one of my old, a 4GO 2666Mhz and its worked but when i started my PC i haved a error from the BIOS saying they failed to initialized before I also tried with only 8GB 2666Mhz still wont...