I do not mean to oversimplify this, but have you tried simply jumping the car? Usually a "clicking" sound without the car starting is a sign of the soledoid in the starter trying to engage, but it is unable to do so due to low power. Checking your battery cable connections for corrosion is not a bad idea either. I have seen batteries in German cars just go bad for no reason one day after working just fine the day before. They build great cars, lousy batteries.