Just because you have never heard of a "serious argument for the non-existence of a god" does not mean that there aren't any. This is called the argument from ignorance, and is a fallacy. Many of the most famous philosophers to have ever lived wrestled with proving god's existence and failed, Derida, Hume, Spinoza, Plato, etc. Even a cursory glance at these writers will show you some of the arguments against a god if you are interested. Most of them are serious and difficult nuts to crack as many of the arguments for god’s existence are riddled with contradictions and fallacies. Equally there are some arguments for the non-existence of god that are preposterous and un-serious. But to say there are none that are serious is incorrect.
I see no proof for any gods; Christians see proof for a particular one and proclaim that this is correct. I must point out again that this is exactly the same for any Muslim, except reversed. Again, how do you prove your god over any other? When you try this thought experiment and attempt to explain why other gods do not exist, you will then see how I feel about your god.