I have a 99 ford explorer and its heating up. I already change the radiator, but know I'm having trouble to get it to start. White smoke was coming out of the muffler when I started it today, but then it stopped and it started heating up again. What could be wrong with it?

Have you checked the oil level lately? Does it need an oil change? I know you've flushed the radiator but how about the radiator cap? That may need to be replaced. Also check to make sure you don't have any broken belts.

Most likely, the aluminum head warped, when the engine overheated, and blew the head gasket. The white smoke is coolant being burned in the cylinders.