What's the FSB on your mobo set to? These are 1600 sticks and their default is prob 1333, guessing your mobo may be at it's default of 800 (FSB), for DRAM to run the FSB needs to be equalk to or greater than the DRAM freq, so could try OCing the FSB to 1333 (this will also OC your CPU, so may have to lower it's multiplier)