1. Try connecting it to another charger
2. Open it and disconnect the battery/fan/speakers etc. (except the charging socket) and try to turn it on
3. Open it and check the continuity of the charging socket wires with a multimeter
4. Check on the board if there is a component that heats up disproportionately (if there is a component that heats up, it must be replaced because it will probably break down)
But usually the problem is the charging socket that needs to be replaced (check with a multimeter the voltage that comes if the socket is wrong)