Did I disable something by mistake?

Hey guys,
On my powerbook, the "F4-F5" volume buttons don't work... F4 is to decrease volume and F5 is to increase it.. the F3 button to mute and un-mute works fine though.
Did I disable a shortcut or something?? Please let me know. neye:

Thanks a lot!

Check your keyboard settings in System Prefs.

try this:

system prefs>keyboard & mouse>keyboard shortcuts>restore to defaults