Why my 97 chevy silverado won't shift out of park when the motor is running or...

[Mauricio D]

...when the key is 2/3 of a turn? It only shifts when the key is 1/3 of a turn then I can start it on neutral and then turn it on then shift to D or reverse and it drives just fine, but if I shift it back to park it won't shift out of park again , unless I turn the engine off again and start over again any help?? Thank you
I already check the brake lights and they work just fine