2003 isuzu NPR Problem

I have a 2003 Isuzu NPR HD. When I parked it in the fall it ran perfectly. Starting it this spring, when I turn the key, the Glow Plug light light up (as is typical) and then it begins flashing steadily. The truck will not fire up. I have tried bleeding the injectors but, to no avail. I know that Isuzu uses these flashing lights as indicators. Any ideas.
What is the sequence supposed to be when the key is turned? It looks as though there is a motor (under the front bumper) that runs a valve on the injector pump. I was guessing that this is supposed to engage when the ignition is in the "on" position. Is this right?
Any help would be greatly appreciated.

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