My acura 2005 mdx will not start i have changed the battery and the starter it started once i replace both parts then i turn off the engine and now it will not start

Check the batter voltage just to make sure it's not a defective battery. You don't want to chase a ghost to find out the battery was drained down for whatever reason. If that's good then you may have a key or ignition issue. This could be caused by a security system. This type of issue does require some hands-on electrical testing. Use this link to find a good shop near you. https://repairpal.com/repair-shops Alex