"Crank" and "turn over" are the same thing. Does it crank at the normal speed, too slowly, or not at all? You might look at the serpentine belt first. If it's okay, check the charging system and battery. Observe how bright the interior lights or headlights are at first and when you try to crank the engine. If they go out, suspect the battery or the cable connections. Do you have a digital voltmeter?