I'll look into this error code today and see if I can nail it down for you.
If the XRes key isn't working though, I'd venture a guess that the APM device isn't connecting to the ultrasound. On the back of the system there should be a rectangular black box that connects to the system with a BNC on the other side that routes up into the APM. If that gets knocked loose or moved around you tend to lose connection to the device attached, as well as damage the CPU board potentially.
I'd look there first and then check to see if the APM is booting up when the machine is turned on.
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