1995 Ford Mustang I hear some knocking!

1995 Ford Mustang 89,200 miles

I bought my car broken down. I put some work into it, like the head gaskets and stuff, and the car was running fine, I had drivin it not to many times before today, but I drove it everywhere and then out of nowhere the engine started knockin, and it had a poppin sound, um I am sure it's a valve thats not connected somewhere, when I checked my radiator fluid it sprayed everywhere and it was over heating! it seemed to lose power alittle like it ran slower what do you think it could be?