Help - major problems?

:crying: HELP-I have a 2000 mpv - just replaced the transmission about a month ago.
Last nite I tried to back out of parking spot and the car started screaching when I tried to put it in reverse-sounded like metal-on-metal and there was a burning metal smell. The van wouldn't go into neutral and wouldn't turn off. I put it into drive and the screaching stopped.
Couldn't turn it off because it would start screaching if I took it out of drive - turning off the key wouldn't help - the van would still run -
I had to remove the fuel pump fuse to stop the engine.
Once the engine was off I tried to remove the key and put the van into Park - immediatley the starter engaged without the key even being turned.
Had it towed to the transmission shop but they say it has nothing to do with the transmission - maybe electrical.
Does anyone know what's going on?
Thanks so much

Hi i was just wondering if you found the problem with your mpv. I have a 2000 myself and am starting to have problems with it. Thanks Tracy