A common misconception, that many people make, is that surge protectors last forever.
The MOVs that are used in a surge protector are sacrificial devices and will lose a little bit of their ability to suppress voltage spikes with each voltage spike that it has suppressed. Eventually the surge protector becomes just a power bar with no surge suppression ability remaining. The good surge protectors (i.e. expensive ones) have a circuit that detects when the MOVs are unable to provide adequate protection any more and will display an indicator light and/or disable the use of the surge protector.
Surge protectors that only use MOVs are suppose to be replaced every year.