My 2500k is stuck at 1600mhz, it was working at stock speed but now it refuses to go into turbo mode. I've checked the bios and speedstep is enabled and also tried resetting the bios and reloading the optimum defaults. Both cpu-z and Asus AI suit report the cpu running at 1600 mhz while running prime 95, the cpu temp is being reported as 38C and all voltages are within the specs. Is it more likely to be the cpu or the mobo at fault?