Then where did G-d come from?
God always existed. He is infinite and did not have a beginning. I'm not positive, but I don't think Time exists for Him the way it does for us. It's why He can claim with certainty to be the Alpha and Omega.
But the Darwinian's failure to answer how life began is not proof that the Darwinian is wrong any more than the Creationist's failure to answer where God came from is proof that Creation is wrong.