Car wont turn over had computer under rear seat replaced ran for a week. Same problem wont turn over had relay replaced ran like a champ parked car came back out wont turn over

Youll be surprised how often people take for granted the basics. Check battery voltage, should be 12.4vdc minimum. If battery is good and still won't turn over, check all battery cables for corrosion and make sure they're tight. If all cables are ok, check for voltage at the starter solenoid small terminal. If voltage is present and still no crank, replace starter. Most of the time it's just corroded or loose battery cables.