Before hippocrates, the ancient greeks believed that abnormal behavior, or madness, resulted from

The answer is Punishment.
They believed that someone that displayed any form of psychological disorders were displeasing the God and the God took their sanity as a form of punishment.
This belief led to many inhumane treatment (such as caging them in public or even throwing them off the cliffs)

The ancient Greeks believed that abnormal behavior or mental illness was caused by demonic possession or punishment from the gods. The Greek physician Hippocrates (460-377 BC) denied this and stressed that psychological disorders or psychopathology could be treated like a disease or injury. He believed that abnormal behavior and illness resulted from internal or biological causes, such as brain dysfunction, head trauma or genetic malfunctions. He is often described as the Father of Medicine in the modern Western world.