1996 Mercury Cougar XR7 engine knock when car is warm.

I own a 96 Mercury Cougar XR7 with 105,000 miles on it. It has the 3.8L V-6 engine. This car has run great for me until recently. I was driving home from work one day when my car suddenly overheated I filled the car with antifreeze hoping to just get it home i was only a few blocks away when it developed a very loud pinging/ knocking noise, it sounded like a diesel engine. It also died on me on the way home and didnt want to start back up again i had to crank it hard and pump the gas for a few minutes to get it started ot make it the last block home. BUt now whenever i start my car it runs fine when its cold and doesnt develop the noise until it warms up. The heat also went out when all this went wrong. I am not certain if this could be a head gasket problem, piston, rings, or just a simple timing problem, I really have no idea where to even start to look to find the problem. Any help you could give me would be greatly appreciated.

Thanks,
Lee