Sticky Keys is a Windows-specific accessibility feature designed to make it easier to use your keyboard one-handed. When enabled, it allows you to use key combinations like "Ctrl-Alt-Delete" or "Ctrl-Shift-Esc" by pressing one key at a time. If it is inadvertently enabled, however, it may seem as though your pressed keys are locked to the "On" position for no discernible reason.
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Press "Windows-U" to open the Ease of Access Center. Alternatively, place your mouse in the bottom-right corner of the screen, select "Settings," and then choose "Control Panel." Click "Ease of Access" to open the same menu as the aforementioned hotkey.
Click "Make the Keyboard Easier to Use."
Uncheck the box next to "Turn On Sticky Keys." Click "OK" to save your changes.