OK, well for people who want me to disprove the existence of ghosts, you need to define what a ghost is. What I believe it to be is an apparition which gives life to the soul of a dead person.
The human brain operates using blood and chemical and electrical signals. When one dies, the heart stop, blood stops pumping to the brain, the brain can no longer operate and the chemical and electrical signals consequently stop.
At this point, the human body is dead, and the "soul" (when I say this, I mean the personality of the person, which what a define a soul as) also ceases to exist.
A ghost is an apparition of a soul; the soul no longer lives, ergo ghosts do not exist.
Furthermore, because the soul has died, there is no longer a way to contact the person, therefore psychics are full of ****.