Xbox one s dead

Hi, I bought a xbox one s as spares or repairs with a beep on beep off fault(power button doesn’t light up). I took it apart and done some checks on the small mosfets and there fine. Even checked the power supply and there reading fine. But all the bigger mosfets are shorted on drain. Today after a few weeks of the motherboard sitting a put it back together just enough to see if it still power on and straight back off off and now the motherboard is completely dead, not even a beep on,beep off. And the bigger mosfets I can’t seem to find find anywhere. I also done done a ohms mode reading on all the ram chip and there all coming back at at around the 58ohms and am sure I read somewhere it should be around 26/26ohms(well for the xbox one s consoles anyway. Sorry for the long post and any help be much appreciated. Thanks