Suddenly my car will not start?

Hello, the starting circuit for this vehicle is a very simple circuit compared to some. Have you tried putting the vehicle back into Park, with just your foot on the brake pedal and key to the on position, put the vehicle to Neutral and then back to Park. There's only two fuses, they are both in the first diagram. And then the Starter Relay and the Transmission Range Switch. I don't think the battery would discharge in 3 hours but try putting the headlights on to see if there's any charge in the battery.
Is the Security light staying on? If there's nothing odd happening, the Starting circuit will need to be diagnosed. The Mazda diagrams are different than the aftermarket diagrams, they show one more fuse (third diagram). The Main Fuse is on the side of the Battery it looks like.
If the Security light is staying on, try locking and unlocking the vehicle again.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Well, that Main fuse being that it's a high amperage fuse is most likely inside a plastic casing and can only be inspected through the clear plastic or pulled out and checked with a multimeter. Do you have a multimeter or 12-volt test light? There are 2 wires going to the Starter Motor, one wire is red with a yellow stripe, that wire comes from the Starter Relay, the other wire going to the Starter should read battery voltage(12v) all the time, so that's the easiest way to check the Main fuse, if the fuse is blown the battery voltage (12v) will be missing.
So that's your first check.
The second would be checking the red/yellow wire while the vehicle is being cranked over. Whatever you're using for checking power, put the negative lead on Battery negative and the other lead to what you are testing. You checked both fuses IG Key1 40-amp and IG Key2 40amp?
Usually if it's a starter failure the starter solenoid will still give the notable "click". So, it sounds like there is something else going on here. But verifying the two wires going to the Starter motor is first.
The engine computer is responsible for activating the Starter Relay and checking computer outputs would be done at the starter relay, to see if the computer is grounding the Stater relay control side.
But in the second diagram, those are the two wires you'll be checking first.
The security light turns off when attempting to crank the engine?

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Well, that was easy, it must have been due to engine vibrations, if you can get a small plastic tie wrap around it to hold it in place, that way it won't happen again. Have a good night.