OK what ya driving?? it could be out of fluid. or the actuator rod could have worn thru the clutch selector fork. and gone straight thru it. check your fluid levels 1st. if they are ok then you need to split the gearbox from the engine and slide it back 6" so you can check the selector fork If it is gone get a new fork and before you fit it weld a bit of thicker steel on the back of it and that'll make sure it doesn't do it again.