I am not Christian but I would like to have an intelligent discussion about religion like what is going on here but people at the Islam forum just post long articles or regurgitation of traditional teachings with no meaningful reflection at all. :/
Anyway, being a monotheist, I believe in the Almighty Creator but I think the question of the origin of God is really about the time line of creation. If God created the universe, what came before Him? I think that the answer might be that our concept of time is off. There is no before.
When God says, "I am the Alpha and the Omega" (this appears in the Quran as well), He is saying that He is the beginning and the end because they are one and the same. Maybe for God, time is one cosmic moment and it is only our limited perception that conceives of time as linear. But the bottom line is that we are created by He who has control over our perception and being. We come from the source and we will return to that source at the "end."