Brien, we don't know about the things around your QMX, which power supply or is there a ground connection from this power supply to your computer. In the moment I don't see a relation to the firmware. So maybe a flaky ground connection between the power supply and the QMX bypassed via the computer and USB cable? Or did you move the QMX PCB a little bit when plugging in USB and "repair" a cold solder joint?
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It would be nice to know how much supply current when you try to switch on without success (and without USB connection). If nearly 0 the QMX is really off and connecting the computer couldn't trigger something from the firmware. If you see something around 100 mA (@ 9...12 V) the controller seems to work but showing no action via the display. And if you see something around 200 mA the controller may stuck somewhere in initialisation.
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Waiting for some more information.
73 Ludwig
