Applications sometimes reduce your screen's resolution, effectively reducing its size. Older programs such as video games may work at a lower resolution, and though your computer should revert its video settings after closing the program, it sometimes does not. Often, simply pressing the "Control," "Alt" and "Delete" keys and then clicking "Cancel" will restore your original resolution and maximize your screen. Otherwise, fix your resolution by configuring your settings through the Windows "personalization" options.
Right-click your computer's desktop.
Select "Screen resolution."
Click the arrow in the "Resolution" drop-down box. A slider will appear.
Click the slider and drag it to the very top.
Click "OK." The screen will flicker and then start displaying its image at your original, larger resolution. A new dialog box will ask you to confirm the resolution change.
Click "Keep changes."