Most older laptop computer screens develop a magnetic charge from the activity inside them. Left alone, this can cause discoloration and distortion at increasing intensity until the screen is degaussed. Where once screens required manual degaussing coils or eraser tape, screens now degauss themselves, either manually or automatically. If magnets are not present and you notice either discolored or "purple" edges on your screen, it can most likely benefit from being degaussed.
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Close out of all programs running actively on your desktop by pressing "Ctrl + Alt + Delete" and highlighting each program in the "Applications" tab, then clicking "End Process." By ending the programs, you will be asked to save information; this data should be saved before degaussing, since degaussing requires turning off your monitor (and therefore, your entire laptop).
Shut down your laptop. While restarting, screens often begin degaussing; other computers will perform this function only upon initial startup.
Wait at least 20 seconds, but preferably more than 30. Turning a laptop on after it has just shut off can cause damage to hardware.
Turn your laptop on, and allow it to start normally. Computers now degauss as part of their startup routine.