You might have played around with a graphics settings recently? Or maybe a recently installed software / game played around with the graphics settings.
If you have an nvidia GPU (and provided you have the nvidia-provided drivers), right click on the desktop, and choose NVIDIA CONTROL PANEL (if it's not there, try looking in CONTROL PANEL).
When a window comes up, on the side you should see a expandable drop-down under DISPLAY. Under that, there should be SCALING. Choose that, and select USE MY DISPLAY'S BUILT-IN SCALING (or if that don't work, choose USE NVIDIA SCALING).
If you have an ATI, although the steps are different you are looking for a setting called SCALING. Same with Intel intergrated graphics. A few restarts sometimes may be required mind you, so have some patience if it don't work the first time round.
Image editor for the Fate/hollow ataraxia English Translation Project (mirrormoon is NOT translating)
DJMax Korea Veteran Elite Member (Top 350)