why cant i start my 2009 mersedes c300 after an accident?

Check auto shut down. If you were in an accident, it will shut spark and fuel to the engine. Refer to your owner's manual for location.

the engine does not turn at all it clicks once and thats it

Then you need to check to first make sure the battery is good, make sure the battery terminals are clean and tight, Make sure the ground to the engine block is clean and tight, and then turn to the starter if everything checks out okay. It may have been damaged in the accident.

i did that but still nothing but what i forgot to say erlier is that a pump goes on for couple seconds then turns off

That could be the fuel pump. It should run for a a couple seconds when you first turn the key.

Try this. Have a helper turn the key to the start position while you check for voltage at the smaller wire on the starter. It should get 12 volts. If it does, the starter is most likely the problem. If there is no power, then work back to the starter relay and then the ignition switch. Also, and you may have mentioned this, check the main fuses under the hood.

Let me know what you find.