if the 2 cables are ok, remove selector from top of gear box (fwd) having first removed the wire connector and said 2 cables, undoing the four bolts to the gearbox. (one at back bit tricky). the shaft should slide round (gear stick moved forward and backward) and up and down along it's axis (gear stick moved left to right). if you cant select gears then this movement is restricted and will need the four screws removed to look inside for broken bits (typically broken bolt).
Peter Pablo B, April 2009