Please, i need software function key for TOSHIBA Satellite C840. i have searched on toshiba site. but, its nothin\'. where i can find this driver? or other solutions.
Not sure which key you mean - do you mean the <Fn> key?
That key, and the <F> keys do not require a driver other than the keyboard driver which is built in to Windows.
It's more likely a hardware problem - a faulty keyboard.