Ok, I'm curious. How does the explanation for everything's existence being "God did it" not simply push the question up a level to wondering how to explain God's existence?
I just noticed that if you replace "God" with "Big Bang", it's pretty much the same question.
The answer to Big Bang is that before it, there was no time itself, so there's no notion of "before" (or if you wish, it's an error in the question itself that assumes there was "before").