If your Proton eye sensors are allowing the marker to shoot with the eyes on and no paintballs in the breech make sure to clean the breech and engine of any dirt, debris, or broken paintballs. Remove the sensor board and clean the eyes and eye pipes if necessary. Any time you have broken paintballs you should remove the sensor board to clean the eyes.
If your Proton is failing to sense balls in the breech and therefore will not shoot with the eye sensors on, remove the sensor board and inspect for corrosion or damage.