More details would be needed for proper diagnostic.
Do you have still current inside the car when key on . EX : radio/blower/lights.
If yes , do they dim down when you "start" the car? , if Yes , could be dead batt or corroded wires.
If it just clicks (when trying to start it) and you still have full juice in the accessories , it could be the starter.
With these questions answered ,people can point you in the right direction.