Might want to have the ignition swith cylinder lock checked out-start here
Friday, May 6th, 2011 AT 9:55 PM
Just to add to this if the key is badly worn down that could be your problem and I would start by having the chevy dealer cut a fresh key using your vin number to get the key code to do it. If thats not the case then try tapping on the key opening lightly with a hammer then see if it turn's. If it turn's replace the cylinder before it locks again.