If Atheism is true, then Everything is ultimately the direct result of purely random, uncoordinated and undependable accidents. Note that "Everything" includes Our Conclusions.
If Our Conclusions are ultimately the direct result of purely random, uncoordinated and undependable accidents, then Our Conclusions are entirely random and undependable.
No Atheist believes that his own conclusions are random and undependable, so no Atheist really believes in Atheism.
What we have seen here is that if Atheism is true, there is no possibility of knowledge. However, knowledge is possible; therefore Atheism is certainly not true.