Kajtek is right! Now, per face value, and some things you can do prior to dishing-out 100 bucks..
A) Is your fluid/filter recent(in the last handful of years old).
B) Can you qualify the level with the appropriate Mercedes Testing dipstick.
D) Open the computer coffin, and inspect the two black skinny rectangular black connectors for transmission fluid intrusion. The connectors are above the main computer with the two to three fuses. Unplug them see if they are wet from oil. If they are wet, the probability of your car is in fail safe limp-mode.
Now, if you DIY on your cars, and this car is your second car, or can afford not running it for a couple of weeks. You can buy your self a Carsoft tester for 50 bucks from China. From this thread:
Also, you could call around to your neighborhood auto stores, some read the OBD II codes for free like some Autozones do. The Mercedes codes can be read from the OBD port under the steering wheel, or in the engine area from the 38pin circular connector. The 38 pin is where the magic is for a transmission reset, but you can find out from the OBD port what is wrong.
Check your fluid level and fluid on the skinny connectors.
Report back what you find.
Best of luck,