Perhaps the processor is not compatible with your current mainboard.
Or your system BUS needs to be higher, however, I believe that is called 'overclocking'.
My maximum System Bus is 200, when I reset my BIOS it dropped to 133 and my processor would only function as a 1250Mhz, so I set it to 166 and it went back to 2100Mhz.
I am not very knowledge able concerning these things.