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OK, if it started before, make sure you check the battery terminals. Even if one of them is a little loose or corroded it will prevent enough voltage from going to the starter while allowing lower amperage accessories to work, such as the lights.
If all looks good at the battery end you will need to check for voltage at the starter. There should be at least 12V+ at the starter while turning the key. If you were getting this clicking sound and several turns of the key to start it before, you could have a starter problem.