Computer change no start no crank

Thats a tough question to answer not being there. Since it was a used PCM, chances are it too is bad. Did it have the EXACT same part number on it?

The part number is exactly the same except for the last alpha character which according to the parts department guy at my local dealer only indicates the vendor of the part.
I could not locate an exact duplicate. I tried for 3 weeks.

If he is sure then it sounds like a bad PCM again. Odd that it would have the same symptoms. Are you certain none of the wiring is damaged on only making contact on occasion? Are you sure grounds are clean and tight? Any corrosion in the PCM plug or pushed in pins?

The used module did not have the misfire that the original has. It simply ran for 5 seconds then refused to start, finally refusing to even crank the engine if I am understanding the technician correctly.
From my research and reading of online forums and what the technician relayed to me it sounds like security features have locked out fuel and starter relays.
Most of the posts I read suggest that the only way to eliminate the problem is to replace both the pcm and the bcm.
Now since both modules are basically computers I do not understand why unneeded features or miss programmed instructions or security features cannot be erased or turned off and properly reprogramed. In other words erased and started over again so that one does not have to keep purchasing modules until you get one that will work.

Usually, the PCM can be reprogrammed. I never had to replace both. Now, yes, there is a security system, but it shouldn't prevent the vehicle from cranking. Did your mechanic at least check to see if it was getting spark and fuel to the engine before we got to this point? Also, I believe there is what is called an auto shut down relay (ASD) on this vehicle. It can shut down both spark and fuel.