If the motor is definitely running yet the wiper isnt moving either one of the linkages in the mechanism is broken/popped off or all of the gears in your gearbox have stripped.
You might want to have a read of this:
http://www.zoiedog.com/hoyt/mbz/wiper-system/300TE-wiper.html
The w201 wiper is the same as in the w124, by the way.