If it is saying graphics card not connected, then you are probably running off of internal gpu.
Isn't starcraft cpu intensive?
What are your system specs, in detail? Cpu plus overclock, RAM amount and speed, bios revision number for motherboard.
What driver did you download for the video card. All of this is necessary to help you out, because it sounds like you missed a lot of steps along the way.
Make sure your cable, whether hdmi, dvi, display port, or whatever you use is properly connected to the video card, not to the motherboard output... Yes, I know it may sounds like a weird thing to say, but many people don't know that just because they have a dedicated gpu, that they actually have to use it.