Why doesn't it start? Changed starter and battery already. Just clicks.

MAY BE A BAD ECM TRY ONE AT THE SALVAGE YARDS THAT HAVE MATCHING NUMBERS AND SEE IF IT FIXES YOUR PROBLEM

A "PCM" will not cause the starter to click.

Would need to start first by properly charging and testing the battery to ensure it is serviceable, make sure the battery connections are clean tight and secure. After that check the starter and starter solenoid that is more likely to be the cause.