Hook the syringe up to the cap top tube, park the heads on the capping station and then pull to see if you get any ink. If you do, it should at least print a little and I would replace the cap top. If you get no ink change the cap top. Also, check the nipple on the manifold where the dampers connect and see if there is a crack or it is broken completely. This would cause the yellow not to fire but the magenta would still work.