Is it OK to believe in heaven and hell but not believe in a god? What if all those things in the Bible existed without the presence of god?

Well if you're approaching it from a Biblical perspective no it makes no sense. There are other religion out there that believe in some version of Heaven and Hell without a deity such as Buddhism and Jainism.

What is heaven without God? Non existent...The bible is the word of God, It does not man anything if that is not the truth of it.

That's just silly, if that were the case then we could probably go wherever we want when we died, we could just walk out of hell and walk straight to heaven since their wouldn't be a god to stop us, we would be lost without God, why do you doubt him?

Kind of odd, really. Heaven is the home of God and Hell the kingdom of Satan, so how can you believe in the place and not the king of that place?

One is free to believe whatever he or she chooses to believe in as long as their acting on the same belief does not harm to any other or to themselves and as long as they understand that believing in something does not necessarily make the same true nor real.

No.

Mk 16:16 He that believeth and is baptized shall be saved; but he that believeth not shall be damned.

no0 its not okay to do that