So, what can I say? There is no single proof which can show the existence of spirits. Indeed, there are tons of vague proves in this field. When we want to convince someone who never believe the possibility of spirits' existence that they actually exist, we have to show several hundreds of cases which strongly suggest the existence of spirits. We'll ask them after presenting tremendous amount of proves, 'How do you explain these cases?' Still, there should be a few people who don't believe it. But they will realize that they don't have enough proves which can stop people believe it.
Anyway, please read the following stories. It might change you.