If you follow the Atheist mindset in the beginning all were Atheists living in a world without RELIGION. What went wrong?

No, con men invented religions in order to obtain power/control over others.

Interesting take on it. I never thought of it like that.

Since someone obviously conceived (invented) gods, and chose to worship them, it can then be said that not all remained atheists.
What went wrong was that belief systems arose and became instruments for mass control and genocide.

What you seem to misconstrue is that prior to being introduced into god-belief (Theism), all human children start life absent said beliefs; by definition, atheist.

Since young children cannot consciously discern belief, there is no such thing as (for example) a Muslim baby, only babies of parents who follow Islam. Belief is an outcome. The need to believe can be innate, but isn’t present in everyone. 

This post was edited by Don Barzini at February 6, 2018 10:40 PM MST

I happen to know the answer, but it is serious. If your question is not serious, I will keep it to myself.

have no idea

What went wrong was when mankind evolved and developed language then the concept of a God began and brought God into existence. God didn't like evolution so he turned time back far enough so he could restart 'the beginning' by creating the Garden of Eden with Adam and Eve et al.