I would check the battery first thing. Almost the same thing happened to me the second day I had my Range Rover. I had been fiddling around, cleaning and such with the doors open and the radio on for a few hours which drained the battery. Then I tried to start to go for a drive but nothing happened when I turned the key, and even the steering remained locked.
If you have a multimeter check the voltage across the terminals of the battery, it should be at least 12.0v with nothing turned on and the key removed. With the key in position 2, down to 11.0V is about the minimum it should be and might be just enough to start the engine.
If you don't have a multimeter open a door and observe the interior lighting and see if you notice it being dimmer than usual. Same with headlamps.
Seems like your steering column is stuck try to unhook the battery leave it for 5 min and hook it back up if it starts then try to turn it off again if it doesn't start again means you have a bad steering column ecu I've seen. One online send you the link