First of all, what is the exactly model of your GPU?, because 7800 is the series, for example 7850 or 7870.
What kind of outputs has your video card?, as I can see you have 2 DVI, but there's another one like HDMI?.
What for did you use a DVI adapter for your main monitor?
You should connect one monitor on the DVI and the other one on the HDMI in case you have it. That must works.