First, car does not start, does the starter crank the motor over? Easiest thing to try is another ignition key,(known good key). The key you have maybe defective or erratic and this will cause this behavior. The ignition keys hold certain coding info and if all the info is not transmitted to the vehicle you can have the symptoms listed. If you do not have another key you may need to order one from MB by the VIN number. The keys are over $200, so at this point you may want to pay to have a quick test of the vehicle by a technician/shop, it may reveal obvious items that may need addressing that the display did not show. Sometimes this is the best money spent instead just throwing parts at it.