First we must wade through the countless definitions of God. Simultaneously we must agree-upon which God we're referring to. I presume by Belief in God, you mean the Abrahamic God shared by Christianity, Judaism, and Islam. This is the predominant religion and belief-system of Earth. There are a few alternatives, and then the Pagan undercurrents which precede it all, but for the sake of this thread, we do not necessarily include those "Gods".
God as Omnipotent, All-Powerful
God as Omniscient, All-Knowing
God as Omnipresent, All-Being
These are the most common definitions I run into, from Theist and Atheist alike. If there is a God, then He must be All-Powerful, or powerful in ways far beyond the comprehension of mere Humans. In the way that New York City must seem like a God-derived place to chimpanzees and monkeys, so too does God exist and persist far above the level of Humanity. By this analogy, even removed from our Human environment, and placed into the middle of Heaven, we would still be at a loss, utterly confused and amazed. The implication of this first analogy is that: the human mind cannot really or definitively know God because of this innate power difference.
God as Immortal, Beyond Life and Death
In the Pagan Pantheon, before the rise and spread of Abrahamism, Gods were believed to be humanlike, Immortal beings. Death does not affect them. Thus they have knowledge far beyond the lifetime of a human, and presence far beyond the lifetime of a human. These Godly Beings also exist in another "Realm Outside" of human awareness and environment. Sometimes, Gods are claimed to 'intervene' and step into the Human environment, temporarily. Gods can 'possess' Humans, "speak through" Humans, as the Hellenes asserted. These claims are a bit more realistic than Omnipotence, but can hardly be proven "Scientifically". This puts Mysticism and Religion in a category other-than Empirical Science. However, both categories can share Rationality to some degree.
God as Ancestor Worship, or Idol Worship
The main shift between the Pre-Abrahamic world, to the Post-Abrahamic (our current time) world, was the general abolishment of Pagan Idol Worshipping. Abrahamic followers were commanded by their God, to destroy all Pagan Idols and Idolatry. Thus they have done so, and successfully spread their religion throughout the known world, to this day. The destruction of an Idol, is the destruction of a Pagan God and its "Shamanism". This co-aligns with the Hellenic notion of Gods and Deities, by their interpretation of Ancestor Worship. By displacing and destroying a Pagan Idol, what you are doing is destroying the memories of their Ancestors. It is the Obliteration and complete Annihilation of a tribal culture and identity.
This process continues today, in what you call "Secular Humanism". Secularization is the destruction of all Sub-cultures, into one worldwide, globalist, Mono-culture. Abrahamism is underneath this, because it represents the spread of the Abrahamic Faith, by its continuation to destroy any and all Opposition.
You must not worship your Kin, your Ancestry, your Ancestors, your Blood. Instead you must worship and kneel before the Abrahamic God. You must be made a Slave to the Abrahamic God. This destruction of your Ancestors, your tribal Idol and Sigil, is your destruction and Rebirth, your Baptism into the Abrahamic fold.
Religions cannot co-exist, but instead must compete to the Death. But this Death is not a mortal death--it is an immortal death. It is a spiritual battle, of Gods, between Gods. Idol-Worship is representative of Ancestor Worship, honoring ones' kin, ones' birthplace, ones' Homeland and Environment. The greatest abstraction of this is within the Roman Pantheon, where Divinity becomes abstracted to the entire Planetary system. There is a God of Earth, of Mars, of Saturn, of Venus, of Jupiter, of Sol, of Luna, Etc.
Now to the point...
Do I believe in "Your God", the Abrahamic God? Well, I don't know. I haven't recognized many, if any, earthly Authorities of Him. I've never met Christians, or Jews, or Moslems, who could present convincing arguments or Reasons for their beliefs. I find the Christian religion, of Jesus Christ, most compelling. The real life, birth, and death of Jesus Christ, is most convincing of the bunch. Was it real? Is it real, now? I presume so. Nothing supernatural needs to be implied though. Humans can do amazing "miraculous" things of our own volition, control, and choice. What is impossible to the masses of humanity, is not so to the rarest exceptions and individuals of humanity. So I leave some room for belief and faith in this.