Will not power up.

My daughters Yoga 900 will not power on. Nothing at all happens when pushing or holding the power button. The battery indicator lights with charger plugged in but no other sign of life. I have had the laptop mostly disassembled through steps in the guide “Charging Port Replacement” and reassembled. The battery has 7.7v so appears good. Is it looking like a dead motherboard, or are there other components that can be checked or replaced first?

Thanks,

Don