If this light is off, it indicates that your surge protector has reached its capacity and done its job, therefore it is no longer able to protect against surges.
When this occurs, you will have to purchase a new surge protector to restore protection to your connected equipment.
Note: this product has no serviceable parts inside
This product, like all surge protectors, has a limited life. Even under normal circumstances, and in the absence of defects, the product’s life will end when the components providing surge protection exceed capacity and cease to provide protection from power surges and spikes.