The ignition switch might be broken. The key turns effortlessly with no resistance, and the car will not start.
I think you are exactly right. The tumblers inside your ignition lock cylinder may be broken as they are usually what locks your key into each position such as accessory, on, or run. Also, if the car will not start, this is another indication that the tumblers may have been knocked out of place as they are what completes the circuit to send battery voltage to the starter. I would recommend having your vehicle inspected and repaired by a qualified technician. Most of the time a new ignition switch will also come with a new key so unfortunately the ignition key will no longer unlock the door but the car will start again.
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