Have you checked your coolant level to make sure you're running full ? Sometimes when you fill the radiator up with a coolant/water mixture, it will look full. However, once you run the car a few times, the coolant and water will fully mix and there will be less in there than you think. Its possible this is why you got the coolant light, because you're not running enough coolant fluid. It could also be your thermostat has failed. Does the car run unusually hot on the temperature guage ?