My initial reason for believing that there is a real God is because the Bible declares it. For the same reason I believe there is a real devil and that he is a clear and present danger. I recognize that this is not good enough for some people, so I will go on to extrapolate a bit. First of all, let's take the indisputable fact that there is good and evil in the world. Science cannot adequately explain why some apparently normal and sane people can commit terrible acts of violence and evil.
Science tries to pin the guilt on the genes, or in other words, all is physical.
This might explain why some people are susceptible to one thing or another, but it doesn't explain why many professing Christians made a complete and abrupt change in their life and personality after accepting Christ as Lord and Savior. We do not see such an event anywhere in the animal world. The physical brain can't be coerced into this complete change against nature with the inducement of wonder drugs and other brain candy or even a lobotomy. However, this change that happens instantly with salvation is so complete that even the instinct to live is ignored to preserve the essence of it. This fact was poignantly enforced with the courageous decision of one young woman at the recent Columbine Massacre who confessed her belief in God though it cost her life.