Check your transmission fluid level to see if the fluid level is full. Do this after driving the car if possible.
Also check to see if the bushings are worn out at the ends of the connecting rod between the shifter and the shift linkage arm on the transmission. If so replace them.
Check and change the filter in the transmission. It may be cloged and preventing the transmission from shifting.
If you cannot do these things take the car to a transmission shop.
1993 190E 2.3
2000 Toyota 4x4 Tundra