Lower Graphics with video card

Aug 14, 2014
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I recently built this - http://uk.pcpartpicker.com/user/nortycrosal/saved/#savedbuild_1368885
My video card was the last part to arrive and did so today. Prior to its arrival i installed windows etc. Now i have installed the graphics card and connected my HDMI cable to it, my resolution has reduced significantly. I turned it off and on but all this did was make the screen smaller. The resolution is better but now there is a black border around my screen. What should i do?