One of the essential characteristics of a black hole is density. This is important because the gravitational field at the surface of an object depends on its radius, so to get an escape velocity greater than c, you have to pack a whole lot of stuff into a really small volume. Before a star collapses and forms a black hole it has to run out of fuel. The force of gravity that tries to contract the star is balanced by energetic fusion reactions that try to blow it apart. For billions of years these forces balance each other and the star is stable. It goes through its life cycle by burning (fusing)progressively heavier elements until there is a tremendous of iron. Since there is no way to get energy out of fusing iron into anything else, the reactions die off and the star begins to collapse. If it is massive enough, the gravitational attraction will be so great that sub-atomic particles will be compressed into a sea of degenerate matter, and the density becomes sufficient to create a black hole. Long story short (I know, too late...) a star can't really become a black hole until it dies, and then it can't really be ed a star any more.