Electrical wiring in your home has a limited life-span. The life span estimated for PVC cables is about twenty years.
HOW TO FIX IT
It is advisable for home owners to replace the electrical wiring when the estimated life-span is over or when the condition of these cables has deteriorated and no longer safe to be used.
A licensed electrician can advice you on the working condition of your home wiring and whether it is necessary for a replacement or not.