car will not start now on 2000 Mercedes-Benz S430

i get a message that my dash is defective
and my gas gauge goes from full to empty
what is the problem

3 answers
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.
there was a recall on the dash cluster. check and see if your car is still covered
I had the same problem it was my alternator, i had to replace it with a new one.