Perhaps it happened when you plugged in or detached an external monitor. Maybe you just hit the wrong key somehow, but now your Windows desktop is sideways, positioned in portrait mode while your screen is in landscape (horizontal) view. You can’t even read the text without tilting your head or turning your display on its side.
Fortunately, there are a couple of ways to fix a sideways screen in Windows; these methods work in Windows 7, 8 and 10.
Fix Rotated Screen with a Keyboard Shortcut
Press CTRL + ALT + Up Arrow and your Windows desktop should return to landscape mode
You can rotate the screen to portrait or upside-down landscape, by hitting CTRL + ALT + Left Arrow, Right Arrow or Down arrow.
Fix Sideways Screen With Display Settings Menu
Right click on an empty part of the desktop background and select Display settings on the pop up menu
Choose a screen to fix if you have multiple monitors attached, otherwise skip this step if you have only one.
Select Landscape from the orientation menu
Click Keep Changes when prompted
