Does anyone know how to unlock "Fn" key?

I have "Acer Aspire One" Notebook.. I don't know how it was locked.. Now when I press the letter "M" on my Keyboard, "0" is typed in.. Similarly a "*" is typed inspite of "P" & so on.. Even right now, as I am typing, I have been pressing this "Fn" key throughout.. & its very irritating.. Seriously.. I mean, I can't type in freely now without my 1 finger on this hell "Fn" key.. Please help me out..