What would prevent car from starting.

I recommend having a professional diagnose it. If it is turning over and intermittently starting, this could be an endless guessing game. You'll want a shop that has the factory Mercedes software to do a diagnostic scan. Here below there is a link to certified shops in your area that can give you a proper diagnosis: http://repairpal.com/mercedes-benz-within-10-miles-of-battle-mountain-nevada-89820