Dell Function Key Lock

If you're running Windows 10, you can also enable or disable the function key lock through the Windows Mobility Center:

If the keyboard shortcut doesn't work, or if you want to lock this setting so it never changes accidentally, you need to change it in the BIOS. dell function key lock

Most modern Dell laptops allow you to toggle this setting instantly using a specific key combination. If you're running Windows 10, you can also

Ensure the Fn key itself isn't physically stuck, which can override your lock settings. If you're running Windows 10