Troubles selecting 1st and 2nd 1990 SW20 Turbo

Hey everyone,
 Haven't looked too far into this one yet. but i was driving on chapple st last night (yeah yeah i know - i was going to the jam factory to see a movie) and in traffic, all of a sudden i couldn't get the gear leaver over to the left to select first or second....  so after a few 3rd gear starts (was almost at jam factory, going over a speed bump fixed the problem.)
 
But it's happened again... not sure what is going on. I've checked the linkages at the gearshift end.  not sure if this is a common problem or not.  SERIOUSLY hope it's not an internal gearbox issue :\ 
 
Any assistance is welcome.
Thanks Guys,
 Haydon.

+1
Check at the gearbox end.
For a quick check, if you lie down beside the car you should be able to reach in, in front of the rear wheel and move the selector shaft to select gears.
The upper cable relates to the sideways movement of the gearstick, and moves the selector shaft in and out of the gearbox, that's the one you're interested in.
The lower cable relates to the gearstick moving forward and back, but from what you said that moves freely.

Sounds like it could be a clutch issue to me...  Might pay to check all that.  (Thinking of Maxim's car right now)

I had both shift cables go on me in the past. Ended up replacing them and all is good.

One thing that may be happening is that the cable has stretched and could be close to breaking.
 
Good luck with the lady friend :)