Question Diagnosing machine that won't post

[Rhythm-styk]

So Im in an interesting situation I got an msi gp62mvr for free as a parts machine since the owner couldn't get it to post. Now I have an identical laptop that does work. Thus far I've stripped the faulty machine down checked every component that I could easily remove(ram, hard drive, ssd, network card, heatsink and fans battery, power supply) every single component from the faulty machine works as intended in the working machine. I also tried a hard reboot tried disconnecting and reconnecting the cmos battery tried powering the motherboard from the power supply circuit of the working machine. Nothing worked. I should also add that I see no discolouration that would lead me to believe there's any obvious water or heat damage to any part of the board. I am an electrical engineering student and I have some experience with soldering and working on boards. Is there anything I can do at this point to diagnose this machine or is this just a lost cause ?
Tl;Dr have two Identical machines. one works and the other doesn't( won't post) I've tried all the obvious things. What do ?

 

[Rhythm-styk]

Just a little more stuff.
All USB ports have power one set is connected to the main motherboard and one Is powered directly from the power supply.
Fans don't spin up whatsoever even tho the power led turns on.