don't you hate it when....

you get a 'new' land rover and the gears disappear 5 miles from home....after a while i got second, but it popped out on overrun, eventually limped home at 19mph......

symptoms: can't engage gears, neutral feels very notchy, like the selectors are out of line....clues?

You havnt had much luck with landy gearboxes 2day have you?!

Maybe we bought the same vehicle!

http://www.landyzone.co.uk/lz/f6/struggling-get-1st-2nd-gear-51922.html

If its the selectors you'll be very lucky, cos otherwise its a total rebuild. Easy to tell though, take the floor & tranny cover out and the gearstick & top plate off the gearbox and all will be revealed.
In fact you'll probably find out for the first time in your life how a gearbox selector mechanism actually works, like I did.

Check that the detent springs and balls (3 off) and the interlocking plungers are all in place as they should be. If all this is all OK then you have a problem inside the box