Belkin Wireless KeyBoard 280 (Wireless Desktop)

Some keyboards which have shortcut keys on the function keys have another key on the keyboard which is used to alternate between the F keys and shortcuts. Mine, for example, has a key called F-Lock just to the left of the F keys. First check for this.
Other keyboards maybe controlled by software which interecepts the F key and performs another function so you could also see if you have installed any Belkin software which you could disable.
Other than that I would suggest sending a quick email to Belkin for support.
Oh and their support section is quite useless as it doesn't even contain keyboards!