I have a 2004 mazda 6s and I left the keys in the on position over night and drained the battery so I replaced it and the car still wont turn on nor will the doors lock orthe trunk open, ?????????

You probably need to re program all the security.

Mazda 6 keys Press the "lock" button on the inside of the door. Press unlock immediately afterward. Insert the key into the ignition. Turn the key to the "On" position, then off again. Repeat the process three times within 10 seconds. Close the car door and open it again. Repeat the process twice more so that you do this a total of three times. On the third time the door should be open. The doors will lock and then unlock automatically. Press the lock button on the remote control key twice very quickly. The doors will lock and unlock as you press the button. Get out of the car and close the door. Test the key by pressing lock and unlock again. You have now programmed the Mazda 6 key. Now that's for the locks anyway, hopefully it will also work for your ignition system I could not find any other way. Best of luck

Same thing just happened to me, NOV 2021 did you ever figure it out?