EDIT: The lack of evidence is what makes me an agnostic atheist.
You deny any possibility of a higher power (atheism), but also believe that said higher power may or may not exist and it's impossible to prove either way (agnostic)? Aren't you contradicting yourself?
Not at all. The terms aren't mutually exclusive. Think about it like this: theism deals with the belief itself, while gnosticism deals with the knowledge.
Atheism is NOT a denial of any possibility, but simply lacking in belief.
Agnostic Atheism is basically not claiming to KNOW one way or another, but lacking a personal belief that there probably is any god
Agnostic Theism is not claiming to know, but believing there is a higher power
Gnostic theism/atheism is belief one way or the other, but claiming full certainty and knowledge of the existence or nonexistence.
I personally think that Gnosticism one way or the other is impossible when dealing with such a claim.
I see no reason to believe that hell exists; there is no evidence, nor any logical argument that makes its existence seem even a slight possibility. However, as ffdthree said, it's impossible to definitively prove this, just like it would be impossible to definitely prove there isn't an invisible teapot hiding behind Neptune right now.
As for God, is it possible to believe in a God and not hell? Well, entirely. Is it possible to believe in the Gods of most religions and not believe in its hell? Absolutely, but you have a much harder time justifying it, because you need a reason to explain why certain portions of your holy text can be taken as gospel, and certain parts can be ignored. Under most religions I think this is just about impossible to do, but of course it's something people try to do all the time.
To be completely honest, you said everything I was thinking (as you probably would have guessed). I just didn't wanna type it all out at 5 in the morning. Sooo, THIS.