What signals the beginning of the events that lead to the end of a a star's life?

When the elements in the star get fused, they go from H to He to denser and denser elements, but when it reaches the the point where it's about to create Iron, that's the brink. The final stage is reached when the star begins producing iron. Since Iron nuclei are more tightly bound than any heavier nuclei, if they are fused they do not release energy—the process would, on the contrary, consume energy. This really messes up the star and causes the star to 'die'.