Resolution ingame problem?

Well i recently bought this monitor http://www.newegg.com/Product/Product.aspx?Item=N82E16824236153 its great! and i pluged in hdmi cable into monitor to my asus radeon hd 6670 GPU.. when i play a FPS game ( A.v.A ) i change resolution to 1920x1080 the whole fits well, but when i change resolution to 800x600 or... show more Well i recently bought this monitor http://www.newegg.com/Product/Product.aspx?Item=N82E16824236153 its great!
and i pluged in hdmi cable into monitor to my asus radeon hd 6670 GPU..
when i play a FPS game ( A.v.A ) i change resolution to 1920x1080 the whole fits well, but when i change resolution to 800x600 or 1280x720 the screen does not fit and makes these thick black lines on each corners, it never happened to me before my previous GPU fitted the screen when i play a game, BUT! when i change view mode to DVI cable the screen fits but not with HDMI mode idk why..
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