If Intel as Rolli59 said, need to go to BIOS enable XMP and select Profile 1, or if AMD they often use what is called DOCP or EOCP - find that, enable and select 1600, may still have to manually set the timings as those don't alwasy work as well as Intel's XMP, or if no DOCP or EOCP then need to manually set up the sticks