The water dispenser is freezing up and you cannot get water our of it.

This is usually caused by frost build up inside the door over time that degrades the insulation value from the backside.

a long defrost would work but would require the fridge off and open for days. you could try adding a bit of Styrofoam to that area inside the door or warm that whole area up with a hair dryer to remove frost. A short length of copper wire (longer the better) placed in the dispenser tube would carry heat up the dispenser tube and help to maintain a flow .