Unlike Santa Clause and the Tooth Fairy, which were imagined purely for fun, the concept of God does have some logical underpinnings.  The strongest reasons to support the God concept are:

1)  Everything needs a cause.  Causality requires time.  Time could not have gone on forever in the past, for if there had been an infinite period of time to traverse we could never have gotten to now.  Thus, there had to have been an entity that was not a "thing."  There must have been at some point in the past an uncaused cause, which is irrational -- not a thing, not something that can be understood that gave a definite beginning to our universe.

2) The universe is extremely complex.  It operates by 20 precise constants, which if any were to change by even a small amount the entire universe would cease to function in any meaningful way.  Furthermore, all material objects from the atom to humans are incredibly complex.  These facts strongly indicate a designer with a supreme intellect. 

Therefore, we are left with the necessity of a creative, thinking, intellect that is extremely powerful and exists in an irrational manner outside of time, actually created time and everything else that is known to us, including us.  We have God -- the prime mover -- the prime cause, and the master designer.

Asking questions such as "Where did God come from?" or "Who made God?" are oxymoronic because the very reason for the belief in the first place is that there must be some entity that cannot be understood.

So is there really a God?

Perhaps unfortunately, but actually no; the above leads one to an illusion of God.  We imagine an all powerful creative being because intelligent beings that make things, like us, is what we are familiar with - we project our characteristics in a way so as to fill our void of knowledge.  All the above can logically lead to is that the universe and life are difficult to understand. 

How do we know there is no God?  Some say it can't be proven or disproven; and a principle of logic is that you can't prove a negative.  A belief in something that is not provable or falsifiable through experimentation or observation is relegated to the world of imagination -- with disbelief being what is logically preferred, but not necessarily untrue; something imaginary could in fact be true.  However, because something is not falsifiable though experimentation does it mean it cannot be disproven.  Any concept that is self-contradictory can be disproven through logic alone, thus it being non-falsifiable through experimentation or observation is moot.  One does not need to disprove something that simply "cannot be."  One does not need to prove there are no square circles, for instance.  The attributes given to the God of the Bible represent self-contradictions and thus render the God of the Bible to not be actual.  

Some self-contradictions pertaining to the Biblical God:

1) All powerful ~ Nothing that is truly all powerful could be motivated to do one thing more than another because no choice from all fathomable alternatives could be considered more convenient or desirable than any other choice.  Any "Being" that is all powerful would have no motivation and could not do a thing because he could accomplish anything in an infinite number of ways with equal ease.  It is our very lack of power that instills needs, determines choices, and in-turn motivate us to act. 

2) Made all things, but is not responsible ~ We are told that the first two people on earth disobeyed God and were punished and we all inherited their sin.  God being the prime mover, would be the prime cause.  He would have made all effects and all affects.  It would be utterly impossible to not be the direct conscious cause of everything that would occur in a universe of your own creation and design.  The very idea of a conscious prime mover would make the very idea of sin itself impossible, as well as atonement to God for wrong-doing because any intelligent prime mover would be the ultimate knowing cause of everything.  God would in fact have to atone to us for his mismanagement.  

3) Knows all things ~ Any intelligent being who knows all things would know what he himself is going to do in the future, so that would negate his own ability to decide what to do. 

4) God is eternal ~ Nothing can have existed forever, not even time itself.  If the past had been infinitely long then that endless time would have been impossible to traverse to get to now.  Nothing can be infinite, not even God.  If God exists outside of time and created it, then he could not have had time to work within it to do anything.

A being that is all powerful and who created us and the universe, and to whom we must atone for wrong doing is simply a mythological belief and does not in fact exist.  People tend to personify what they do not understand, and thus far have invented over 30,000 gods, nearly all of which assume human form and traits.  Human's were not made in God's image, he was made in ours -- though the mere belief in something can be as significant as the fact of its existence. 

Aside from the God of the Bible, could there be any supreme intellect that created all things?  The answer to that is not unless one believed that such a being is the ultimate knowing cause of all that happens, which logically is what he or it would have  to be.  

In all fairness the logic we began with needs to be dealt with.  There must be some factors that are in some sense god-like, and difficult to understand, but probably not actually incomprehensible.  Nature itself is presently beyond our full understanding, and someday we may have a better understanding.  Perhaps the universe creates itself in a sense by revolving in and out of time.  The 20 constants that control the universe may in fact be ultimately related and just find a natural equilibrium, which is exactly what is postulated in string theory.  The complexity found in nature may be due to an ongoing processes of evolution based upon fundamental principles of logic that just must occur, and it all occurs out of ultimate necessity because nothingness is impossible.  The God-Being we imagine was born from logic dressed in fantasy.  The only true God can only be the dictates of logic, the reality of what must be, which we will come to have a better understanding of as time goes by.

~Brother Mark       

"I contend that we are both atheists. I just believe in one fewer god than you do. When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours." -- Stephen Roberts

Christianity as antiquity.-- When we hear the ancient bells growling on a Sunday morning we ask ourselves: Is it really possible! This, for a Jew, crucified two thousand years ago, who said he was God's son? The proof of such a claim is lacking. Certainly the Christian religion is an antiquity projected into our times from remote prehistory; and the fact that the claim is believed - whereas one is otherwise so strict in examining pretensions - is perhaps the most ancient piece of this heritage. A god who begets children with a mortal woman; a sage who bids men work no more, have no more courts, but look for the signs of the impending end of the world; a justice that accepts the innocent as a vicarious sacrifice; someone who orders his disciples to drink his blood; prayers for miraculous interventions; sins perpetrated against a god, atoned for by a god; fear of a beyond to which death is the portal; the form of the cross as a symbol in a time that no longer knows the function and ignominy of the cross -- how ghoulishly all this touches us, as if from the tomb of a primeval past! Can one believe that such things are still believed?

When irrationalists such as Christian fundamentalists claim they do not believe in the idols of pagans because such beliefs are nonsense and fruitless, but invent their own invisible one, then that also makes them hypocrites.  One idol is made of plaster and imagination, while the other -- just imagination.  What is the difference other than saving on the cost of plaster?  Do we have any evidence that the invisible one does any more than the plaster one?  And, what is the conceptual difference?  Would the real plaster one fail to spring into action if you mistakenly pray to the false invisible one, or would the real invisible one fail to spring into action just because you mistakenly pray to the false plaster one.  If one believes in God, then what's in a name?  Is a real God going to refuse to save you, just because you got his name wrong and called him Zeus instead of God or Jehovah.  Everyone who believes in a deity is either all correct or all wrong.  There is either a supreme Being or there isn't.

Brother Mark

Argument for the non-existence of God

Argument from evil: There is a large amount of suffering and evil in the world. This is incompatible with the existence of an infinitely good, omnipotent God; therefore, God does not exist.

Argument from delusion/superstition: There is a lot of evidence suggesting religious belief in deities is merely superstition or false belief originating in the complexity of the human mind.

Argument from evidence: There is little or no evidence to suggest that a being with the properties of God can exist. Therefore it is more likely than not a God doesn't exist.

Argument from 'projection': God is merely a mental concept upon which we project our hopes, fears, emotions and beliefs. God therefore exists only in mind, but not in reality.

Argument from materialism/naturalism: The material/natural world is all there is, or at least, all we can know. God therefore is at least unnecessary, or at most, non-existent.

Argument from morality/meaning: One can live a perfectly moral and meaningful life without referring to any God. Therefore the existence or concept of such a being is not needed in moral conduct.

Argument from comparative religion: There are countless religions in the world that posit the existence of one God, many Gods, or no Gods. They cannot all be right. Therefore, if your religion is wrong, and another is right, your God doesn't exist. Or, compared to another religion, your claims about God are nonsensical. Therefore, your God's existence can be ignored, or treated as an act of faith.

The argument from 'agnosticism': We cannot prove the existence of any God(s), therefore, we can get along as best we can without one, or suspend judgment until we find better evidence.