I have an a8 3870k with an asrock a75m-itx motherboard. I just got a r7 240 for it but the computer is still using the igpu on the a8 3870K. The HDMI is plugged into the r7 240 and gpu-z says I am still using the igpu. Can someone please tell me how I can get the computer to use the r7 240 instead?