Turning a computer screen sideways results from using the screen pivot feature and is fixed by holding the CTRL and ALT keys and pressing the up arrow. Screen pivot is often used on monitors that rotate to use portrait mode and devices without automatic screen rotation.
Screen pivot was first intended for designers and developers to see long pages by pressing CTRL, ALT and the arrow keys. Screens on Windows computers can also be rotated using the control panel and screen resolution options. Screens can typically be rotated using the graphic card's control panel and selecting the appropriate options. The graphic card's control panel is accessible by right clicking on the desktop menu, but manufacturers also often add shortcut icons in the computer's system tray.