What existed or what happened before that point can only be speculated upon. It's more likely that there was something before this point, and not nothing, like some infinite process which the universe, finitely or not, is a part of.
Oralloy, per what InfraBlue said, what yours, or anyones understanding is can only be speculated upon.
No one can state with certainty "there is no such thing as before the BB"
To my personal way of thinking, the idea that there was no such thing as before the BB smacks of magical/supernatural thinking. Same as when someone uses the same sort of thinking as the explanation that "well, Something/Someone had to cause it."
The only certain answer is "I/we don't know"
However, the idea that there is no before and after, just a different presentation, as InfraBlue said, "a point where the physical laws became viable to its evolution to what it is today" pretty much eliminates the idea of some Other, or Something that made the BB happen.
A young girl produces only a small amount of estrogen. At a certain point the hypothalamus starts to produce gonadotrophin releasing hormone and estrogen production increases, resulting in womanhood. Of course we can see the girl, and the later woman, but that time frame when this happens in pretty much a BB. No one knows for certain what makes the hypothalamus decide "todays the day" We can speculate, maybe someday we'll know for sure. However, it's the same idea that the physical laws became viable to it's evolution of what it is today.