Here are some questions;
1. Have you a spare set of keys, and have you tried operating the locks from the trunk or the passenger door? I don't mean to suggest this as a solution, but that information can tell the members here whether the problem is isolated to the driver's door, or is more involved.
2. Did you notice recently any stiffness or grinding as you were turning the key? What is the temperature where you are?
3. You say the locks don't operate. Is it easier to turn the key than it used to be?
4. Have you tried pulling the key outward with slight pressure as you approach the 12 o'clock position? Can you feel a detent, or notch when you do that?
MB 1986 190D in my past
MB 1987 300E on the street
MB 1994 'Smoke Silver' E420 in my driveway
1999 Mazda Miata in the fun stable
1964 E-Type Jaguar Coupe- Sold
1970 E-Type Jaguar Coupe- Sold
1968 Corvair Monza Conv. with Turbo Transplant- Sold
1986 Merkur Xr4ti- abandoned
various mundane American autos
If I'd known then what I know now...
Hell, I'd probably still have done it anyways.