Mercedes Benz repair: Mercedes Benz 300 TE, mercedes benz 300, auto help

Question
My car will not start.  When I try to start it,it makes a short hum then nothing. It does not make a clicking sound just a short hum. I tried to jump it, no luck.  It has also been getting terrible mileage.

Answer
Of Sharron . Help me 2 help you.
Quick explanation. Here is how it works ok.
1) car cranks but does not start. This means that when you turn the key the vehicle is heard cranking but will not start
2) no crank no start . This means that the vehicle is neither heard cranking or anything at all.

I do not understand hum.
Do this turns your headlights on . Then turn the key and let me know if the lights dim out?

Let Me know
Ralph
Miami Auto Help Inc