Is atheism self-contradictory ?

[Angrboda]

I firmly believe that without assuming that some absolute power created our mind, nothing can be said or done, nothing can be proved or refuted. Therefore the fact that I can demonstrate logical statements and discern between sound and unsound arguments is proof of this power's existence. Where am I mistaken ?

You are mistaken in believing that the only source of a reliable but imperfect mind is a perfect creator. As I'm sure that you are aware, it is postulated that evolution is responsible for the minds we enjoy. You reason that evolution is a random process. This is where you are mistaken. Evolutionary mutations are random. The pressures of natural selection are not. It is plausible that those animals whose minds did not model reality faithfully did not survive as well as those animals whose minds did faithfully model reality. Thus, minds that accurately reflect reality evolved. This is the definition of truth most commonly used, that our statements reflect some fact of existence. The way our minds evolved to reflect reality means they embody truth. That's how you get a reliable mind from the process of evolution.

As a side note, both my argument from evolved rationality and your argument from rationality make one important assumption, that is, that our minds are indeed reliable. That is mere assumption and isn't reasoned towards, for obvious reasons. If you can help yourself to an unjustified assumption, then so can I.