Traditionally, the big bang is thought of as a four dimensional explosion of physical matter and energy.
"Before" the big bang is a bit misleading since this event could be seen as the start of time. In fact, I think the whole linear progression model we use to understand this may be misleading in that it dictates a "before" and "after" simply because we have specified an event.
It is the same that happens when we speak of "outside" the universe. Our understanding of the concepts "inside" and "outside", and our spatial orientation makes it seem a fair question what is "outside everything".
For myself I tend to think of the big bang as the first and only conscious moment in the history of the universe. Every other event is a sub-division of this moment, and the universe itself is a "thought" happening in a field of potential quantum configuration. I am thinking of consciousness here as a chain reaction of information, a non physical attribute to the big bang, the contrast by which physical matter takes it's form and distinction. Not something that evolved within the physical world, but something that is as fundamental to reality as matter itself.
I know this is very speculative and intuitive, but it serves to give a different perception by which it is perhaps easier to see the big bang as one ongoing and indivisible moment. In it we are perhaps able to identify states of being, or moments, that fit in our conceptual layout as before or after or somwhere in between this explosion. But this linear quality that we sometimes assign to it may be entirely provided by the conditions of our perception, and not an attribute of the described events.