I don't believe in God because my parents told me to. That's foolish. I was raised in a Christian home, but I have faced many challenges since then and made decisions about my beliefs on my own.
I don't believe in God because I have never studied other religions/don't understand philosophy. I own a Koran and am familiar with the content of the Hadith. I appreciate that postmodernism is an incredulity to all metanarratives and see it as a useful approach to understanding some physical and metaphysical truths. I know the Universalist arguments and those of the atheists. While I don't claim to be an expert, I find that I know these various religions/beliefs/worldviews better than the average person I meet and these studies are reflected in my point of view.
I don't believe in God because I am unaware of supposed problems with the Bible. Christianity is based on the Bible in many ways so, naturally, I have spent countless hours scrutinizing the scriptures trying to find out if the critics are correct when they say that the Bible is flawed and thus cannot be Holy. (Have you ever studied the Tyndale, Wycliff, and NASB translations side by side looking for discrepancies? I certainly have.) My studies have served to strengthen my belief that the Bible is accurate and not flawed.
I believe in God because I know Him. That's not a hyperbole. I know God as I know my wife and my friends. As a young man I knew His influence in my life and in times of doubting and questioning I still know that He is God. In my darkest hours when I wonder how God can exist in such a dark world I know that the voice I hear is that of God and that He loves me. The experience of other Christians and the words of the Bible confirm my experience, but such confirmation is not needed; I know God.
It may sound magical or new age or silly, but it really doesn't matter to me. God isn't a theory or a stained glass portrait in a building, He is my friend and savior. Is this experience real or just my imagination? I've asked myself that, but the idea is as silly as asking if your brother or sister is part of your imagination. He's someone who walks and talks with me each day in a way that I cannot understand, but years of critical analysis and challenges have convinced me, and many others, that this experience is real.