I believe that there can never be a proof (as in mathematical or scientific) to Gods existence, but there exists compelling evidence in favor of the argument that God exists.
The two reasons for the argument that there can be no proof to Gods existence:-
1. The human brain has limits: I believe that God is something so complex that it is impossible for the human brain (because it is not developed enough) to comprehend it fully. In this era of scientific development, the fact that the human brain has limitations may seem inconceivable. To understand the point I am trying to make, just try explaining the Theory of Relativity to a ten year old.
2. Proof and faith cannot co-exist: Faith is the foundation of all the religions. If Gods existence can be proven, then there is no space for faith.