We don't believe God exists.
Yes, there are common threads running through all the world's great religions, because all religions are meant to help us develop knowledge of God, an understanding of our relationship to Him, and ultimately love for Him. The Srimad-Bhagavatam (1.2.6), one of our scriptures, says that any religion by which men can attain loving service unto the Supreme Personality of Godhead is to be considered genuine.
So in many religions you will find people who understand, as we do, that God is the omnipotent and omniscient Creator, and that He shows Himself to those who serve Him with faith and love. In the Bhagavad-gita (10.10), Lord Krishna declares, "To those who are constantly devoted to serving Me with love, I give the understanding by which they can come to Me."
God does not show Himself to atheists. To fulfill their desire He remains obligingly invisible, generously providing them with the knowledge of how to deny Him. This is the Supreme Lord's compassion. Even when you deny Him, He reciprocates with you.
But although the Supreme Lord does not try to disturb your atheism, sometimes His servants do—because it is, in fact, useless and impossible to deny God, who is the Absolute Truth. As soon as you adamantly state, "There is no Absolute Truth," you have asserted that your statement is itself absolutely true. Therefore, either in affirming or in denying the Absolute Truth, you prove that He exists.
It is also interesting to note that because you are a dedicated atheist, you are drawn to carefully read Back to Godhead magazine—a publication completely devoted to God—just so that you can doubt and attempt to refute its contents. This goes to show that not only the faithful and knowledgeable but even the ardent atheists are fully absorbed in thoughts of God. It is too bad that your thoughts are so negative, but, again, because God is compassionate, even these negative thoughts will ultimately have a beneficial effect on your life.