hmm.. well first thing to ask i guess is, is it a rod type linkage or a cable type linkage?
if it is a rod type, maybe one of the pins that hold the linkage in place has rusted through and caused the rod to pull off. easy fix.. just put it back on and use another split pin to hold it in place.
if it is a cable type, have a look to see if the part where it connects to the gearbox has popped off. (one of the ball joints), also check to see if the 2 cables are still mounted to the car bodywork (or is it the steering rack with a cable type) because if they are not the cabels will just move and have nothing to push against to move the gearbox selectors with.
my knowledge with the cable type linkage is not as good as the rod type though.
