Engine shut off. will not crank

What is the ODB code you get that states you must reset the ECU I wonder.

What's missing ? Fuel ,spark , compression ? How many miles on the vehicle ? Does it have spark , pull a plug wire while cranking an hold it near a good ground . Put a fuel pressure gauge on the vehicle , is there fuel pressure ? Do a compression test , 150 psi . engine mechanical problem . timing chain .

The 3.8 liter engine has a timing chain. The distributor shaft should be turning if your timing chain is still intact. Have you pulled it out and reinstalled it? Maybe you did not get it seated right.
This must not be a '99 Silverado as shown in the heading? Give a reply back, and explain please. You replaced a fuel pump in the gas tank, and now the distributor shaft is not rotating? There is no plausible relation between the two-please explain.

Most likely The fuel pump is going bad. Also the engine oil running below 1 quart can cause engine shut down(Engine Oil Light). The fuel pump and low oil shut down will not register a fault code. The cheapest approach to your problem is to, Make oil level correct, change air filter, change fuel filter And add 1 can of B&G44K to a full tank of 91 octane fuel. This additive is the best on the market and only available through dealerships(Do not use substitutes).The B&G will condition the fuel pump and injectors and increase MPG. and improve drivability.

The knock sensor will not cause a no-start. The knock sensor only retards the timing when the engine is running. If the starter is not working we need to check the battery voltage, battery cables, starter, engine ground, neutral safety switch, ignition switch, security system. These are the only things that can cause a no crank.
If you really have the urge to clear your computer disconnect the negative battery cable for 10 minutes.

Fuse good? I think its ecm1 or ecm2 fuse? relay good? it should turn on for 2 seconds when turning key on. the relay turns the pump on for 2 seconds, then the oil pressure switch powers the pump when the engine is running. when the pump would not shut off, the oil pressure switch could have caused that.

The best way to help find the problem, is to have a fuel pressure test done on it, that will tell if the fuel pump is weak, or the fuel pressure regulator is malfunctioning. If the pressure is low, the fuel pump is weak,
if it is high, the fuel regulator is at fault.

check then crank positon sensor, it control the fuel system. it tell the engine computer when to send fuel

try checking for a shorted or open battery cable..maybe a bad connection somewhere..........check the main ground cable from the battery as well as the body ground.......(use a set of booster cables..put one end on the neg side if battery black or red.......put the same end that you put on the battery on a metal part of the engine.......to complete a temporary ground circuit....do the same with the body).....may be worth a shot..........
hope this helps...Good Luck!