The shifter display indicates a different gear than the actual gear it is in

I have GMC Envoy SLT 4WD 2005 It Will not start, I noticed that The transmission indication on cluster is R while the actual Shaft lever is on P and locked. I tried to start the car or mover the transmission shaft lever both wont work. This happened when I came back from work. In fact I wanted to park my car infront my house then I used break to stop car and parked it. I wanted to move the trasmission shaft to park and stop the engine, I noticed the shatft lever move freely like it was losse then put it on P and turned off the engine and remove the car key. One hour later I wanted to start the car IT wont till now. Please could you help