Why doesn't it start?

SOURCE: cold start valve problem

if you have an electric cold start valve make sure to unplug it and if keeps apling fuel with electrical conector unpluged that means the valve is not good, but if not then you have an electronic problem, possible a bad cold start sensor or cold start module or cicuit problem, and might be a time to take it to an electrical shop

SOURCE: merc 190e fuel injection problem

If the fuel gets to the distributor but no fuel comes out of the distributor if the airflow disk pushed into the air/fuel mixure body, i suggest you check the electro-hydralic-actuator
Its the black box (picture thanks to elproboscis from ebay america) as it controles the flow to the pluger body inside the centre of the distributor and goes from the plunger direct to the 4 outlines.

SOURCE: C320 not starting

If you hear a slight hum in the gas tank when you first turn on the key for 2 seconds the pump is working. Have the fuel pressure checked by a mechanic, it should be about 60 psi. It's usually located just before the injectors. Also have each injector wire pulse checked (light test) to see if there is enough spark to them. Have the ICM Ignition Control Module unit located under the rotor checked for enough spark also. My Trans Am had the same problem, turned out to be a shorted out injector causing it not to fire. If you can get to the wires to the injectors, pull one at a time while cranking to see if it starts or not. If you find that one that's faulty and unplugged the engine will start. That would be one problem. Also have the cars CPU checked to make sure it is not faulty also.

SOURCE: Runs for 20 minutes, gets hot and shuts down. Still has spark

I had the same problem, took to a benz dealer, it was the fuel pump relay, cost for repair $200.

SOURCE: mercedes E300 turbodiesel, 1999, is poor to start

Yes sir , you have a failing valve, soon it will snap in two....please have your head checked. You can do this yourself by placing a long-handed screwdriver , business end down to each cylinder while pressing your ear to the handle(while engine is running)...you will notice a definite difference when you hit which cylinder has the bad valve. Also makes sure the egr valve is clean and your exhaust recycle valve is not stuck.( located in the crossover pipe)