My Garage Door (Challenger 9300) will not open due to the sensors not functning. WIll open while holding,Help?

The door will open normally, but will not close unless the on in the garage is held. The red light on the sensors will not illuminate to display that they are aligned and the light on the motor portion flashes when you just try to push once to close. Can I just get new sensors? Or is that a waste of money?