The clicking comes from the starter solenoid, which indicates a lack of battery power. So, if using jump leads cures this, the fault has to be within the battery itself, the terminals being loose or dirty, or maybe the alternator isn't supplying the battery with enough electricity in the first place. If you have a multimeter, put this across the battery terminals with the engine running. You should see around 14.4 volts if all is well.
John
May 2009