Board Thread:M.U.G.E.N Help/@comment-28896136-20160814205020/@comment-3495717-20160814210733

Some function keys have two features, the primary feature and a feature when used in conjunction with the Fn key (F4 on my laptop can either do what F4 is supposed to do or put my laptop into sleep mode); it is likely that your computer reverses the functions of these keys, meaning if you wanted to use F1 to KO the opponent, you'd have to press Fn and F1 at the same time, as it sounds like F1 is some sort of mute button by default.