The type of person who asks 'ah, but what happened before the Big Bang?' is, as Stephen Hawking once noted, like someone standing on the South Pole wondering which direction is south.
Part of becoming a grown-up intellectual being is the recognition of boundaries.
Nevertheless, the question is not completely invalid. The Big Bang may have been a local event within greater processes, which strain everyday concepts like before and after.
Confronted with grief I have resorted to a more subjective explanation of time, but the truth is that it is rooted in both our conscious and unconscious selves, as biology makes no sense at all without time.