My Big Question

My question is about the very existence of this universe. Everyone knows about the Big Bang theory. But what caused the big ka-boom? What triggered it? Did the Big Bang even occur? I want to know the very reason that is responsible for all the stars and galaxies and for us all to even be here. To make it simple, if the Big Bang Theory is true, what caused the Big Bang?

Update: Here are some sites relating to my big question

http://www.space.com/31192-what-triggered-the-big-bang.html

http://www.universetoday.com/116835/what-came-before-the-big-bang/