Let’s start by clearing up some confusion. (1) While some people may think of God as an old man in the sky, that is not the notion of God in the Judeo-Christian-Islamic tradition, nor that addressed by Aristotle or the Buddhist Logicians. For us, God is an Infinite being. (2) “Infinite Being” does not mean, “really big and powerful being.” It means completely unlimited being.

Dynamic Ontology

Dynamic ontology is built on the notion of being can be explicated as the capacity to act. A finite being can act limited ways, and an Infinite Being can do any possible act. Finite beings can act in this way, but not that; here, but not there; now, but not then. Infinite being can act in all possible ways in all pos­sible places at all possible times. So we are not God and have forgotten it, because forgetting is a limitation on our ability to think. Nor is the universe God because it is constrained by the laws of nature, which are more restrictive than what is logically pos­sible.

Dynamic ontology helps us understand the distinction of essence and existence. Essence, what a thing is, is the specification of its possible acts. But, a specification does not normally entail that what we specified actually exists. Existence adds a new note of comprehension: that the thing we are talking about can act in reality. Not only does it have a specification, but that specification is operational. Perhaps an analogy will help. Essence is like a photo­graphic slide. It specifies the picture on the screen, but there is no picture on the screen until the slide is illuminated. Existence is like the light illuminating the slide. It makes the projected picture actual.

Background

To prove existence we need to show the capacity to act. We can only show this by pointing out a concrete act that must be attributed to the being in question. We know concrete acts only through experience.

Thinking something does not make it exist. So “proofs” such as St. Anselm’s ontological argument fail because they only prove that if we define God as the greatest possible being, then we must think of God as existing. But, thinking of God as existing does not make God exist. We can think something in two ways – with commitment to the thought and without commitment. The ontological argument does not show that we must be committed to the thought that God exists, but only that to be consistent, in the context of the definition, we must think of God as existing.

We can only prove what we know implicitly. Proofs show us how to assemble facts we already know to see something we may not have noticed. So, we can only prove God's existence if knowledge of it is implicit in experience. People with good intuition can see it directly, but may not be able to articulate it for others. Those of us who are less intuitive, or who trust intuition less, need step-by-step guidance to come to the same conclusion. A proof will make the connections needed for us to be aware of God in our experience.

Finally, this proof assumes a working knowledge of logic that not all may possess. For example, the Principle of Excluded Middle tells us that complete disjunctions like “A is either B or not B” are always true if they are meaningful.

The Proof

Premise 1: Something exists.
This is a fact of experience. At least I exist (cogito ergo sum), so let’s take our self to be concrete.
Premise 2: Whatever exists is either finite or infinite.
This is a complete disjunction. Remember that “finite” means limited in ability. I am finite because I can’t do everything that's logically possible, but only what is physically possible for me.
Premise 3: Any collection of finite beings, including the universe as a whole, is finite in being.
Again, finite does not mean quantitatively finite, but limited in its ability to act. Even the whole universe is limited in its ability to act. If it were not, logical possibility would be the same as physical possibility and physics identical to logic. There are logically possible acts that the universe cannot do. Since it has finite dimensionality, the directions in which its parts can move are limited. It is logically possible to move in more directions, and so the universe is at least limited in this way. Even if the universe were spatially or numerically infinite, it would still have a limited capacity to act. Since the universe (or multiverse if you subscribe to it) is the largest possible collection of finite beings, any smaller collection will also be finite.
Premise 4: If a being exists, its explanation must exist.
If this were not true, science would be impossible. If things "just happened," the observations would not be underlying dynamics, and could neither confirm nor falsify hypotheses. Note that “explanation” has two senses: (1) the fact(s) that make some state of affairs be as it is. (We may or may not know these.) This is the sense I am using. (2) Our attempt to articulate our understanding of (1). This is not the sense I am using here.
Premise 5: If something exists, its existence is explained either by itself or by another.
Given that explanations exist, this is a complete disjunction: the explanation is the thing in question, or not the thing in question.
Premise 6: A finite being cannot explain its own existence.
Why? Because whatever can be explained by a being, viz. whatever a being can do, results from its essence, the specification of its acts. For a finite being, existence, the unspecified power to act, is logically distinct from its specification. I am human and I exist. Being human explains my ability to think, because that is part of what it is to be human. But, being human does not imply that I exist. If it did, no human could cease existing.
A thing is finite because its specification or essence limits its capacity to act, its existence. What limits is not what is limited, viz. existence, the bare capacity to act – just as a slide limiting light differs from the light it limits. Logically, limits negate specific acts, while existence does the opposite, making acts operational. When essence limits existence, existence is more comprehensive. Something less comprehensive, a finite essence, cannot entail something more comprehensive – existence. Thus, a finite essence cannot entail existence -- a finite being cannot explain its own existence.
The distinction of essence from existence does not apply to an infinite being, if it exists. Why? Because an infinite being’s capac­ity to act is not limited by what it is. For it, no possible act is negated by its specification. So for an infinite being, what-it-is would be identical with that-it-is.

Further explanation of Premises 4, 5, and 6:
A being is necessary when it is. (Once it is now, it is no longer possible for it not to be now.) Since finite beings have a history of coming into and going out of existence, the necessity of their present existence is not intrinsic. (It is possible for them not to be.) So it must derive something extrinsic – their explanation. Therefore, every actual thing has an explanation even if we are ignorant of it and say, “It just is.” Our verbal explanation is not true unless there is it reflects reality.

Conclusions
Conclusion 1: The existence of a finite being implies the existence of another being, its explanation. P4, P5, P6.
Conclusion 2: This other being cannot ultimately be finite. P3, P6
Any collection of finite beings, taken as a whole, is itself finite and so requires a further explanation.
Conclusion 3: So, the existence of a finite being implies the existence of an infinite being, as its explanation. C2, P2.
Conclusion 4: Therefore an infinite being exists, which we call “God.” C3, P1.
We are free to name things as we wali, but calling the infinite being “God” corresponds to common usage.

All of the commonly ascribed attributes of God (almighty, omniscient, etc.) follow from God's unlimited capacity to act. For example, if God were not omniscient, then there would be a logically possible act, reflecting on an item of information, which God could not do. If God knows, God thinks and so is personal in the sense of being aware, etc.

Note that this does not show God as existing and acting in only the past, but as the present and on-going explanation of all existence.