Can my key be reprogrammed in the ignition - 1999 Mercedes-Benz E-Class

The electronic key which you have only need to programme once, then it will work till get faulty not necessary to re programme there are only one way to re programme, it's only can do with new electronic ignition switch replacement so if you replace new ignition switch insert your key in it and it will take few minute for programme it take all the programme automatically then you can turn the key and start the car,
If you don't have replace the ignition switch but key is not working it's faulty either key or electronic ignition switch, if you have any other additional key if the car start with that key it's very clear it's faulty your key which is not working give me more details do you have the other key and only not working one key like that, however first replace the battery for your key and try if not work put a comment i will give you more details,