I'm quessing, but you are probably using a SB-e CPU.
To use DDR3-1600 you must either
1) Go into bios and select use XMP, profile one which will auto set speed to 1600, and CL values to correct values, also set the voltage t correct value.
2) manually set parameters.
SB specs are for DDR3-1333, and using DDR3-1600 will Void warrantee if by chance your CPU dies and you need to RMA it (may depend on the rep you talk to). Intel does sell a OC warantee that covers" exceeding Vcore of 1.5 V, exceeding Ram voltage of 1.575 V and exceeding ram freq of 1333 (ie for i5-2500K it is $25. Ram Voltage of 1.500 is fine.
PSS. I'm running DDR3-1600, CL7, @ 1.600 V on a i5-2500K build - have NOT bought the OC Warentee.