Any guesses as to why this car won't start?

2006 Honda Civic - we installed a new battery and replaced the starter with a remanufactured one from Auto Zone. After that, not even the lights would come on when turning the keys in the ignition. We took the starter back to Auto Zone, and they found there was a crack in it, and gave us another one, which we installed. But the car still won't start. Is it fuses? Alternator? Voltage regulator? Should we try something else, or just take it to a repair shop. Thanks.

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