My C300 2009 will not start. Please help

I have a 2009 C-300. Last week went for regular A service, they also
changed FLEX DISC for $440, saying it was cracked.
This morning car wont start. I will have to tow it to dealership next week. My
battery is original Mercedes, changed 18 months ago. I read online, some
said its ignition switch or may be steering lock or even starter relay. But
everyone had slight different symptoms. So I will explain mine in detail.
When I insert key, I do not hear the zzzzip sound. The key TURNS
NORMALLY. ONLY cluster display comes on, showing date & mileage. But
Engine or gas or ABS light does NOT come on. The gear shift is locked.
Windows do NOT roll down. Dash board back lights are on, but when I
switch the headlights on through the knob on left, the dash lights go away,
come back on when turn headlights to off or auto position.
I thought it was the battery since the headlights wont turn on and the dash
lights turn off thinking headlights taking all the juice. The voltage on battery is
12.25 V. My friend brought his X6, we connected cables, but still EXACTLY
the same. Even the headlight won’t turn on despite being connected to the
other car, I checked the voltage and it was 13.75 on the terminals (while
connected to the running bmw).
I checked the starter fuses, 6,7,19,27. They are OK. I saw a video describing
similar problem caused by starter relay, but in that video the engine, ABS
and gas lights were turning on when turning the key, mine does NOT. So I
did not buy a relay as it may be a different problem.
I am just trying to save money on towing it, if it is something that I can fix at
home. I have a fear that it would be one of those $1200 thing everyone is
taking about with the steering. Please advise me if you can ….. thank you in
advance.