Why don't my 2002 Pontiac Montana,s motor turn over after I replaced

I bought this 2002 Pontiac Montana, with a 3.4 motor, the owner had hit a deer on the passenger battery side and everything was replaced, the battery was not getting recharged from the alternator so I replaced it with a new one, not rebuilt, but still had same problem and the check engine light never came on but all the other lights doe's, dome, headlights, dashboard lights all work. I plunged in a code reader and it won't come on. I plunged it in the cigarette lighter and it's still don't come on but it works fine when I plug it in the house so I know the code reader is okay, all fuse's, and relays are good as long as the battery is charged the van starts and I can drive it but, now after installing a used ECM module the van won't start and I installed it according to the procedure the way you're supposed to install a different ECM, I jumped it over on the starter with a screwdriver and it started only for a second then stopped, I did it again and it stopped, I did the whole thing over and I got the same thing. So what is wrong?

In the beginning when I first got the van it already had this problem and the person I bought it from did not know it as well because she had hit a deer on the passenger side front where the battery, fuse/relay box and most of the main cables are. The van set for 2 years and finally got all the parts replaced that were damaged. She charged the battery and sold the van to me and I drive it home, the next day when I drove it in about 20 minutes the battery went dead and when I checked the alternator was bad so I replaced it with a new one, not rebuilt and when I checked after I started it up I was only getting 12 volts not 14 that told me that the battery still was not getting charged so I checked all relay's and fuse's and there was nothing wrong that is when I noticed there is no check engine light on and there should be then I plunged in my code reader and it did not come on I plunged it in cigarette lighter still don't come on even when motor running so I knew that is a good sign that the ECM had something wrong with it so I replaced it with a used one and when I said I did it according to procedure I should have said according to one person's procedure. After I installed the ECM module, and hooked battery up I wanted 15 minutes, I then turned key on that's when I saw I now have a check engine light and I let it stay on for 5 minutes with out trying to start it. I then turned key off waited another 5 minutes, then I tried to start it but nothing happened no sound of any kind I rechecked fuse's and relays and battery is full charged but with the ECM module it did have it would start and run but only off of the battery but when battery ran out of power the van had to be recharged again to start and run and there is no check engine light, after changing ECM I have check engine light when key is turned on but it won't start. Do I need to do something else with the ECM so it will recognize the system before it will make contact?