I am trying to fix my moms van for her because she can't afford a shop to do it. she hadn't done a oil change in 3 years I came to find out. It began because it died and wouldnt start at a gas station. Easy fix I thought changed out the starter and it fired up no problem. but the oil was leaking almost as fast as I put it in. So I started looking for sources. Changed out the oil pan gasket and rear main seal. Then I found that the majority of oil was coming out of a sensor ( the vehicle speed sensor), went and got a new sensor and started to switch it out, this is where I got into the areas I'm not familiar with. In order to gain access to the bolt to remove the old sensor I had to remove the arm that runs from the transmission to the shifter inside the van. I was worried about doing that but there was no other way to get to the bolt. Got it changed out and everything put back together and went to test drive it and I put it in reverse and it wouldn't go anywhere put it back in park and the shifter won't come back into reverse or any other gear, and the van wont turn over.
It seems like you may have the shifter linkage put back in incorrectly. The van will have a neutral safety switch. If the transmission isn't in neutral, it won't start. If you got the linkage on wrong, it may not be going back into park/neutral and the ignition won't let you start it. You may try shifting it to which ever end (keeping your foot on the brake), then try to start it. If it doesn't start, click it one notch and try again. Do this through the full range to see if you can get it started. By doing this you may be able to tell if this is your issue as well as what you might need to do to get it right.