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.
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.
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Click "Make the Keyboard Easier to Use."
Uncheck the box next to "Turn On Sticky Keys." Click "OK" to save your changes.