My FN Keys do not work properly (Sony Vaio)

Hello guys,I'm having some trouble with my sony vaio and I was wondering if you could help me
My "Fn" keys do not work properly.When I use them to change the sound of my laptop there is no problem(Except for not showing the sound bar,it just lowers the sound.),but when I try changing the brightness it does not work at all and I don't know what is causing this :(

My Vaio model is VPCEA3CFX
Thanks already,guys :)

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