I agree with the suggestion that your key is worn out.

This problem is not exclusive to diesel models, affecting all 1998 and newer models with the electronic key.

It happened to my mother's '99 E430, and the local Mercedes independent, MB Stars, explained that it is not an unusual problem.

When you insert the key, the car might not recognize that it is the key programmed for your car, so nothing happens.

If you have a second key, try it, and see if the problem goes away. It worked on my mother's car.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".