I’ve replaced the motherboard in my XE500C21-H04US. I did this because the power adapter broke on the original...

It took a while to convince myself, but the display was the issue. I guess I just got confused because there were no problems with the display when I went back to the old motherboard … until just recently. Plugging in a secondary display confirmed that all was well. The new motherboard is working fine and does not really need anything special to activate. After I completely unplugged and reinstalled the display everything was visible and working normally!