|Several possible issues here:|
1. The mains adapter/charger pin-plug (which plugs into the laptop charging socket) may be damaged, or it's cable damaged. Remedy = new mains charger/adapter.
2. The charging socket on the laptop may be faulty'damaged. It will need to be looked at by a laptop repair shop.
3. The battery may have "died" and can no longer hold a charge. This can happen if you leave the battery in place when using mains-power for long periods (you are supposed to remove the battery in those circumstances). Additionally, even if used properly, the battery will not last forever. New battery required.