Caravan starting problems

Several months ago my wife drove our '96 Dodge Caravan to a friends house. The van would not start when she attempted to leave. It turned over, and all the lights worked but it just wouldn't start. The engine
would just turn over, it wasn't catching at all. It seemed like there was either no gas or no spark.
I had a local repair shop tow it to his business. It was the same guy I had purchased the vehicle from a couple years ago. He said that he saw that there was some corroded wires and that he was in the process of replacing them. At one point he said there was no way he could charge me the labor that he put into the vehicle. I asked him on several occasions how much I owed him and he just continued to say that he wasn't going to charge full labor and that he would be done with it in another week. Weeks turned into months and the van still wasn't running. I wasn't pushing him at this point because my wife lost her job and we didn't have the money to pay for it anyway.
We recently rectified the money/job issue and have resumed pressure on the mechanic. several weeks ago he said that he needed to replace the computer so I picked one up on Ebay to save some cash. He put it in and he said that the van started but cut off after about a minute. This is all it would do. He tried another computer and it did the same thing. The mechanic is now telling me that he believes there is some kind of security system that has been enabled by changing out the computer and he needs to figure out how to disable it.
Could this be the case? If so, does anyone know how to disable the engine shut off? If this is not the case then what else could it be?
TIA, Gary

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