Under general relativity, there is no 'before the Big Bang'. The problem is that time is itself a part of the universe and is affected by matter and energy. Because of the huge densities just after the Big Bang, time itself is warped in such a way that it cannot go back before that event. It is somewhat like asking what is north of the north pole.
The conservation of matter and energy states that the total amount of mass and energy at one time is the same at any other time. Notice how time is a crucial part of this statement. To even talk about conservation laws, you have to have time.
The upshot is that the Big Bang did not break the conservation laws because time itself is part of the universe and started at the Big Bang and because the conservation laws need to have time in their statements.
