well at this point the only thing i know to suggest is to run a 'self diagnostic' on the machine manually using the 'onboard' diagnostic.
This is the manuals suggestion when there are no error codes present on the display but no machine operation.

It is a fairly simple test routine using the 'run/diag' switch on the logic unit.

-disconnect battery
-remove logic cover
-discharge head capacitor bank
-remove drive fuse
-release parking brake
-place 'run/diag' switch in diag mode
-reconnect battery
-turn on key

there are several steps to test, if the step passes test it will advance on to the next step, if there are any failures it will not progress until you identify the fault and repair it. To skip a test step just toggle the 'run/diag' switch and it will skip the current test and move on to the next test.

on the inside of the rear cover is a truck diagram sheet which should include the diagnostic steps telling what each one is.
If the truck does not advance to the next step on any of the tests that circuit must be repaired.