If by the "ball" you're referring to the type of flow gauge that works by a stream of gas pushing up a small plastic ball in a clear tube or drilled piece of clear plastic, then the ball is either stuck somehow (moisture in its tube might do that by causing some friction), or it's showing there's no flow of oxygen enriched air, meaning the concentrator itself is not working. Can you feel some air flow if you hold the outlet towards the skin on your cheek?