Urgent help needed

Finally got my landie back on the road after a few weeks with the points going. Running fine, come to go out in it today and I put it in gear, and it gets stuck! Cant move the gearstick either with the clutch in or out, clutch is still operating, but I seem to be stuck in 3rd gear.. HELP!!!

yer first port of call wants to be yer detent springs which am located under the top cover of yer g/box.
take the g/baox cover off and you'll see th etop cover under the gear stick.
take the two 'L' shaped plates off ( springs) and the center bolt which has another spring under it.
now remove the cover and make sure all they interlock 'doo daas' are free to move. grease it all up and re assemble making sure the balls are round and the springs are springy and not broken