At Atheist Wisdom we read:
Much of this question can be discarded. It boils down to "How can we believe in anything?". This question should be more unsettling to the theist than the atheist. The answer is that, philosophically, we can never be certain about anything, but we can test ideas by repeat measurements, theories, models and verification of predictions. God fails these tests, whereas my hypothesis that "if I drop a brick on my foot, it will hurt" is based on past experience and my knowledge of the world. Science works.
Maybe God, in whom I believe just is not subject to scientific testing. See Atheist Wisdom: Questions from Believers