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The usual cause is a stuck key in switch inside the barrel. Remove the key and try lubricating the barrel with a graphite lube and also turn the steering wheel side to side. If it is still stuck then that barrel will need to be replaced.
The barrel is easy to replace but in order to release it from the column you will need to turn it to position 2. Since it will not turn you can remove the steering column covers then pop of the ignition switch. Then you can try to move the end of the barrel then push in the release and pull it out.