At this point, I decided to test it out before screwing everything back
together again. So I screwed in the motherboard with just one screw,
connected the power supply, and plugged it in.
The green LED blinked twice and started the fade on and off cycle.
Pressing the DISPLAY button on the remote did not turn on the
Xbox. Pressing the power button on the Xbox itself did work. Holding
down the power button turned off the Xbox and began configuration
mode of the XERC 2 SE.
Something looked to be wrong with the IR receiver, but there were only
three wires, and I have pictures to verify I didn't mess up the colors.
It is a good thing I made the IR receiver wires long so I can flip
the motherboard. It's only three wires, but I'm lazy. Lazy is why
I bought the XERC 2 SE in the first place.