My car wont go into gear, as if the shifter is moving in a circular motion instead of grid what do i do?

1988 Porsche 924s, drove well yesterday, then at a stop today wouldn't go into gear, i can move the shifter all around, but as if there is no "grid" for it to fit into. not sure if this is a gearbox issue or what, i need to figure out why this is happening so i can know what to fix. thanks!