Because you gave a very simplistic and naive argument.

I mean how did god come about? Did he create himself? That's a paradox. You can't create yourself.

The universe either came from nothing, i.e. created itself, or it was always there. The same could be said for 'god'. A god wouldn't have to fit in with any laws of the universe we adhere to, it could simply have always existed. There are parts of our universe that do not fit in with the conventional laws of physics.

And there is no proof of god,yet there is proof of the big bang.

There is no proof for the big bang, there's just evidence that points towards it being the most viable theory. There may not be any evidence that points towards an existence of god, but that does not mean it can't be a theory.

SO explain to me how a ancient book can tell the truth and could be altered a hundred different ways? It's sillier to say that god could be a possibility.

You never mentioned a Christian or any other religion's god originally; a possible existence of a god doesn't have to have anything to do with any current religions which are all undoubtedly wrong.

It's sillier to say that god could be a possibility.

Its silly to say that there is a god. It is not silly to say there is a possibility of a god. Even with an infinitesimally small chance of a god existing, that is still a possibility.

Now, I don't believe in god, or a god of any form, but if I was going to refute someone's claim, I wouldn't do it using straw man arguments.