Overclocking gpu problems

So just now i downloaded evgas precision x to overcclock my two gtx 670ms, and I set a overclock for 770mhz and a 1600 for the memory, i then started up crysis 3 to see what kind of boost I would get, black screen nothing it was just a black screen. has any one else had trouble with precision or just using overclocked sli graphics cards in crysis 3 or is it a problem with the gpu or driver.

Go back to stock speeds (assuming that the stock clocks are 598core and 1500mem) then overclock in small increments. Overclockling mobile gpu's imho is asking for trouble. 

I'm gonna have to agree with this. Most mobile platforms barely have the internal cooling to keep things cool at stock settings as it is. Unless you've got a kickass cooling pad, I would just as soon skip it. Better to suffer that little hit in performance than to damage your components and jeopardize the lifespan of your machine.