could anyone help me, I have the late 2015 iMac, 5K, 27” model. The computer is not booting up. When i press the power button i can faintly hear the fan working but no chime or display. Keyboard does not light up also.

I opened up the computer and on the 4 LED lights, only 1 and 2 light up (display still connected). What should I look for as far as repairs? I have my own phone repair service and I have plenty of micro soldering experience repairing iPhone boards. I also have all the tools available but I do not know anything about how to fix iMac boards or where to start looking on the board. Any help would be appreciated!

I swapped two screens from one to the other on the iPhone X and Face ID stopped working on both. ill try later to see if swapping the proximity sensor fixes the Face ID not working.

iv tried today to swap screens on two iPhone X without swapping over any parts, just the screens and Face ID stopped working on both. ill try later to swap the proximity sensor to see if that fixes the Face ID.