Clicking is a sign of low battery voltage, voltage drop (due to dirty or loose connections) or resistance/failing starter or starer solenoid . Have the battery tested to see if it is OK, perhaps it will just no longer hold a charge. At rest before you start the car the battery voltage should be 12.6 volts if the battery is fully charged and does not have any electrical load accidentally staying on. If the starter solenoid is failing it may be cheaper to replace the contacts and plunger rather than replacing the entire starter.