Stop at a red light got ready to go when the light turned green my car would not move forward nor back. Check transmission fluid it looks good no burning smell what could be the problem.
Sounds like a internal problem ie. torque converter, or fluid pump not working. These parts failing would not allow pressure to be built up inside the transmission to make it shift or move. You wouldn't get a burnt smell, because it wasn't slipping and the clutches are fine. You will need to take to Transmission shop to be sure.
RepairPal Certified shops can diagnose and repair your 1990 Mercedes-Benz 420SEL. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.