Sensors do fail without throwing codes as ghost says,
The 02 sensor could flash up and dissappear in a second in 1000 miles and the only way you'd know is if you ran a diagnostic,
I'd hazard a guess to the crank sensor failing more than a cam sensor if it's turning over but not firing, where abouts are you ? Maybe someone local willing to 'lend' you a sensor so you can swap it and see if the fault goes,
That way you can narrow down your fault without spending unnecessary money and time,
Maybe worth having a look at the sensor in situ may have a damaged or loose wire, it's at the front of the engine, shine a light in between the pullies next to the alternator
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