As a guess given the post you probably have a PowerShifter model with an enclosed transmission.
An enclosed transmission with an internal problems is usually fatal as they are too time consuming to pull and complicated to work. Most homeowners or guys who mess with stuff would not attempt a fix. Having it repaired by a shop would be prohibitively expensive.
The shift mechanism under the dash could be the problem although rare. If linkage you can get the service manual online and go through that but it’s tough to set.
To distinguish if a linkage or internal problem disconnect the last connection to the enclosed gearbox and try and work the shifter. If it moves then the problem is internal, if not then external and fixable.
