Won't start. Break pedal hard

Hello, the brake pedal would be hard as there is no vacuum pressure for the power brake booster capable of making braking easy -- when the vehicle is not running. As far as not starting, there are any number of reasons why this could be happening. For one thing, the battery may be low in charge and unable to crank the engine, or could be failing. There are engine performance concerns that could be preventing starting. What is the vehicle doing when pressing the start button? Give some further information so we can help.