I have a 2001 Mercedes Benz E320. It was running fine and I got a dash warning to "check battery/alternator for low power" and then about a mile later the car died. I have a portable generator so I gave myself a jump and the car started but died about a mile down the road. I got it towed and bought a new alternator for it. CAR STILL WOULDN'T START, so I bought a new battery for it. Car still won't start! HELP!!!!
Your climate control unit has a hidden menu that will allow you to verify voltage. Take a look at this video, it will show you how to access the menu.
If the electrical system is healthy (sufficient voltage, strong cranking, spark verified) then the next step is to verify you have sufficient fuel pressure.