I have a 1994 Nissan Pathfinder and the tranny won't go into Park so what is the problem and how do I fix it?

Will the selector lever in the cab click into Park, or does the selector lever not reach that position any longer?
If it physically cannot reach the position and lock into it as per usual, then the linkage underneath needs adjustment.
if it reaches and clicks into Park position but the transmission does not lock, then there is a problem with the pawl not tngaging and locking the trans.
Always try to adjust the linkage before delving into the trans in cars something is worn, broken or has slipped put of position.