My Toshiba C800 laptop (12.04lts desktop) has special function keys as follows:
fn+
F2-BRIGHTNESS DOWN
F3-BRIGHTNESS UP
F4-DISPLAY SELECT
F5-TOUCH PAD on/off
F6-PREVIOUS
F7-PLAY/PAUSE
F8-NEXT
F9-VOLUME DOWN
F10-VOLUME
F11-MUTE
F12-WiFi on/off

F6 to F11 (media player keys) work correctly, but the keys from F2 to F5 and F12 are not working.

Why would some function keys work, but not others? What can be done to fix this?