firstly make sure the nose of the key is smooth and clean on the lens. hold the key flap open on the ignition switch and see if there is any lint in there.

Also make sure that you can see the gauge cluster screens light up when you open the door, if it does not then your electronic lock is highly suspect.

If cleaning the key does not work - try the spare key (if you have one) or buy a new key.

Your MB dealer can also test your key - if you are USA based, your Dodge and chrysler dealer can also check it for activity but not sell you a key.

If the car refuses to respond on all the above you are in for an electronic ignition switch replacement which requires a dealer visit - nothing else works because the part is hard coded from Germany and shipped to the dealer at which time it is installed on the car and the old keys are permitted to it. (I think it already has the key information because the dealer keys are also coded from the master build list of the car)

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)