The function keys allow you to perform special tasks in Windows applications. These keys execute diverse functions based on what program you are using. The Sony VAIO laptop computer allows you to control settings specific to the laptop computer with Fn shortcuts. The Fn key can be used in conjunction with another function key to adjust brightness, switch monitors, magnify the screen and alter other hardware settings. VAIO laptops use the ACPI (Advanced Configuration and Power Interface) function to control the hardware access like brightness or volume control. Installing or upgrading Windows operating system can disable the Fn key requiring you to reinstall some drivers. You need to install and activate ACPI drivers which make hardware status information available to the operating system for the Fn key to work.