Hi and welcome to the club..
The shift lever works on a cable, and it could have slipped or broke..
first I need a bit of info..
When you move the lever, do the selector lights work?
do you feel any movement with the car as if it tries to select a gear?
There is a list of items to check in the manual.. most being worn items
in the gearbox, but your answers to the above will help.
John