200 base clock is pretty high... Also depends on what multiplier you're using. Hyper threading. Turbo. Turn off HT and turbo... those are going to require significantly more voltage to run. Still not working, either keep giving it juice or lower the multiplier. It'll take lots of Vcore AND Vtt. From my experience OCing 15 750, Vtt/IMC is needed for higher base clock/speed while Vcore is needed for higher multipliers/having turbo and HT will also need more vcore.