it might not be a Benz but my sister had that high squeal noise you speak of and the cause was that a nut was loose

now i'm not a mechanic so bear with me in my explanation

the serpentine belt goes over something right? well the screw that holds that something was loose hence the noise as the engine speed increases

like i said bear with me on the fact i have no idea what to call it :-)

as for the car not starting, i would check with the battery first then the alternator and starter....also check the conditions of the wires themselves