Proving God and Knowing God
As I have talked to atheists, I have thought that proving God's existence is a little like trying to prove to the other person that he is really awake. One cannot logically prove that we are not all dreaming, but by experience we have great reason to believe that we are not. I believe I am awake (and not dreaming) not because of blind faith, (there are many reasons) and yet I cannot logically prove to you the point fully. Knowing God is consistent with logic - it makes sense, but it is more than that - it is experiential. Unless one has the experience of knowing God truly he or she will never be convinced by the logical argument. However, if we do truly experience God, we will also see the foolproof logic of knowing Him by His Word, the Bible.
My challenge for atheist/agnostics: Try to know God by experience. Seek Him in prayer and through the Bible. See if he is real by pursuing Him as if He is real, not as if He isn't.