1) Do you use two 6pins pcie connectors for the 270x? And which model PSU do you have?
The PSU may not have enough juicy for the 270x, because the whole system will use total Wattage about closed to 450W something. 270x=290W, CPU maybe 95-125 W(?), MB=40W, DVD/CD=30W.
2) Check in the BIOS, do you disable the onboard video card HD4250 or not?
3) Monitor the cpu temp, because the GPU run cool.