Unique Problem Now That It Is Cold Here in GA
 

I go to the car, a 2004 Mercedes C240 4Matic, and use the unlock button on my fob. Works fine.

Put the key fob in the ignition. The car lights up with the odometer showing the miles and the park key on the red dot.

Turn the key to the on position and the dash lights up.

I twist to start it up and... nothing.

The dashboard instrument display stays on. It's almost as if the car is acknowledging the key in the ignition. But not the key actually turning to start up the vehicle.

Any help with this would be most welcome. Thanks, and I hope you have a warm week ahead.

Try moving the shifter to the neutral position and starting it after turning key to the accessory position. I am not familiar with that model but sounds like a case for shifter bushings or neutral safety switch.