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Make sure the battery is good and fully charged. Check the battery cables for corrosion, clean and tighten them. All good there then you would need to test down on the starter to see if there is power going to the small wire when someone turns the key to the start position. If there is power there, then it is a starter problem. You could try and tap on the starter with a hammer to see if it takes off, but still, there would be a starter problem even if it did. No power to the small wire try replacing the starter relay.
Also, make sure your gear selector is fully into "Park" or "Neutral".
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