What do you do when the hood release does not work and you can't get to the engine?

Depends on the cause. If cable is broken, bend a coat hanger to snag the cable still attached to the hood latch and pull it out. You should be able to open the hood simply by pulling hard. If it has become disconnected, like I am dealing with now, it will depend on the make & model as to whether you can release the latch from underneath with a long screwdriver to having to unbolt the latch mechanism after removing the grill.