hi there, can i know what motherboard you are using? if you are using ASUS, Gigabyte motherboard, you should access to it's bios setting, and it will have a core multiplier, in which setting it would result in a change of clock speed. i.e.~ 42x = 4.2ghz. and also, search for vcore setting, for an i5 2500K, (which i have previously,) i would set VCore = 1.30V, core multiplier = 42X. in my previous low end Gigabyte Z77M - D3H.