[HMacmillian]

I have a 96 LSI with the stock transmission. Since late spring it would drop into neutral or into 3rd on its own or with the slightest touch. It would generally do this when I had stopped at a light. Also the shifter itself would move without having to depress the button on the shifter.
Tonight while stopped in a parking lot it dropped into second (according to the dash display) and became stuck. I drove it to a friend's place so I could try and fix it. When I tried to cycle the shifter I could move it forward but the transmission did not seem to shift and the dashboard display showed that it wasn't changing gear. I pulled it back thinking it might reset it and the dis[lay now says it is stuck in first.
I then took apart some of the center stack so I could get at the shifter assembly to see if I could do anything. I managed to use a screw driver to shift the stalk into park. When the tow truck arrived I tried to get it into neutral and I believe I succeeded because it just rolled onto the truck.
So I have two problems,
1) What is wrong with the transmission/shifter? Is it the assembly or something else?
2) Is there anyway I can reset the car's computer to actually see what gear it is in? I had to pull the battery because the wheel had locked and I mad to push the car into the driveway and that did not reset the computer.

If this gets really expensive I might have to part the thing out but that would break my heart so I really want to avoid it.