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