No scientific means exist yet that can effectively prove or disprove the existence of God/Allah/Goddess/Flying Spaghetti Monster/etc. This leaves the matter strictly one of faith and belief. Many people find their beliefs affected by major events: one who survives a deadly car accident may take this to mean that God has saved them, while one who loses a loved one may take it as proof either that God does not exist for "not answering prayers." This is a long-debated matter, but you really have to figure out for yourself if you believe there is a God/Allah/Goddess/Flying Spaghetti Monster/etc.