Overheating and will not start

I was driving and the light came on for check water temperature. I stopped the car and called my mechanic and told him everything. He said to pour some water in the radiator which I did and it was working fine after that but then after two days of not driving I turned the car on and drove less than a mile and the car started heating up again. I applied the same method of adding water but now my car will not start.