What does it mean when abscess goes rock hard? what can happen?

Puss under pressure.: Abcesses are puss under pressure. They get very hard when there is no way for the abcess contents to drain. Generally they will try to break through to an adjacent structure or through the skin to relieve the pressure. If this is not possible they will become rock hard and very painful. Eventually all abcesses rupture and bring great relief, but a scalpel is sometimes helpful.