Something is disconected 'the linkage',lift bonnet, look down to the right of the engine block, at the back,you will see two cables spread in a 'Y' shape with a 'banjo end (propper term)they fit on two pins on a plate on top of the gearbox,one may still be connected the other one will be off,when you push the gear lever forward (1st,3rd)one of the cables pulls the plate on the gearbox to select gear,when you put it in 2nd 4th the other cable pulls it back,put the cable that is off back on to the pin 'presto'.Not a great discription but I fixed my daughters in 2 minutes,still working 6 weeks later,but you should get the ends of cale fixed.
Rich
December 2011