1991 Mercedes Benz 190e wont start

The car is at a repair shop and had the head gaskets the water pump and timing chain replaced. I went to get the car today and the car was running at the shop for 15 min. Then quit. The car will not start.

Why don't we check if its a fuel or spark problem and don't wait for it to cool down do below immediately to catch it

Disconnect a sparkplug wire or 2 and ground it to the engine atleast 3/16 in away from ground have helper crank engine over-do you have a snapping blue spark? If so-you have a fuel related problem, check the fuel pressure to rule out the fuel filter/fuel pump/pressure regulator and listen to the injector/s are they pulsing or hook up a noid light. No snapping blue spark continue to troubleshoot the ignition system-power input to the coil/coil packs, coil's resistances, cap and rotor /distributor pick-up coil, ignition control module, ECM, Ignitor camshaft and crankshaft sensors- Note: If it doesn't apply disregard it