I just have bought a new Lenovo Ideapad S400u notebook, and it is not default F1-F12, it is default mute button, refresh, more brightness, less brightness...
I've downloaded "Lenovo Keyboard Slim Fn Switcher" or something like that, but it didn't work.
Then, how can I change Fn function to get my F1-F12 buttons? I'm running Windows 8.1.