I'm not sure what could cause that, but you can give this a shot.
Right click on My Computer, go to Properties. Under the advanced tab, click Performance Settings, and click on Adjust for Best Appearance.
Worth a look.
i5 2500K @ 4.6GHz / Cooler Master V8 / Asus P8P67 Evo / 8GB G.skill DDR3-1600 / Zotac GTX 780 3GB / Seasonic S12-650 / Samsung 850pro 256GB SSD / Corsair 600T Graphite / those cheap 1440p Korean monitors