This is another problem which is becoming common as the PT's are getting older, it seems to be due to simply wear and tear, but this can be accelerated if you have a large, heavy keyring or a bunch of other keys attached to your ignition key.
The symptom of this problem is the key turning on all the dash lights but not starting the car. If this happens to you, try pulling the key out VERY slightly as you turn to start the car, or to get you home, get someone to give you a push as the car will bump start.(manual gearboxes only)
NOTE In some cases you may have to stall the car to stop it as the switch can fail in both directions
To change the switch follow this video
The video is taken on a lefthand drive car and on the car I changed one on the Lock Cylinder Housing Cover had some sort of sensor attached to it. I'm not sure what this was, maybe its something to do with the immobilizer or as this was a automatic car,it was something to do with the inhibitor which stops you starting the car up in drive
Be very careful with the new switch, that little spring can pop out at any time!!!
In these shots you can see the extra electrical plug attached to the Housing Cover that is not in the video
That little spring at the bottom right can pop out at anytime ! Dont worry as long as you can find it, it will go back together