I am trying to overclock my Core i7 870 to somewhere near 3.75 - 4.0 GHz
It is possible that your CPU won't run at that speed. You should start slower and work your way up. I don't know how this CPU compares to the i5-750 but I built 3 of them, 2 of which would run at 3.9 but the 3rd one would only run at 3.8. I would recommend that you start yours at 3.4 or 3.5, if it boots then test it for awhile, then move up by 0.05 or 0.1GHz and try again.