Unplug your foot pedal. Blow in the hole and wipe the plug end.push the foot pedal plug into the machine.
also, check to make sure your foot is all the way down before starting your next piece. My Janomes will beep and not sew if the pressure foot is not down. Several of my Janomes have multilevel pressure foot lifters, so make sure your foot lifter is firmly down before sewing.
Sometimes foot pedals are faulty. Try a different foot pedal from a dealer or a friend who uses the same janome foot pedal.