No crank no start issue

Hi everybody, hope everyone having a great day. I need some directions on go about trouble shooting my ford expedition 2003. I went to pick up my son from school last year, while I was waiting, I turn the engine off thinking nothing was wrong. After my son was buckle in, I turn the key to start the car. It crank and came on, only for 2 seconds, then it went dead. I thought must be drain battery, so we walk home from there, I came back with the battery jumper and it did not help. I car remain dead. All lights and signal still shine bright, no anti theft flashes check engine light on and car would not crank or start. So I hammer the starter and tried to listen for fuel pump. Nothing… no changes so I ended up towing it home where I remain working on it. I check sensors, I’ve change alternator and check starter, everything look ok. Finally I had a chance to check the wiring from battery to ground and positive wiring also. I even change the fuse box hoping that be enough. Still nothing. Unplug pcm and plug harness back in one at a time. The first one went in, no change, second one went half way in and I got starter to crank but still no fuel pump. Third harnest got same result. So I jump fuel pump relay and crank the car. Still doesn’t kick on. Now I don’t know what else to do. I’m lost and about to give up on the car but that’s my only transportation. So if anyone out there who has same problems or know how or what to do, please shared your thoughts and help me out. I can’t afford to take it to the shop, I barely making end meets… so I appreciate everyone for their time and efforts. Someday good will come to those who help others… thank you