How far along the loading of the track do you get? The first thing that loads is the sky file, then the track and finally the cars, so judging by how far the status bar gets you can tell whether the problem lies with one thing or another.
Have you tried the track with different cars?
Have you included a different sky file?
Does it only crash with your track or with others?
If you create a different track, does it also crash? (try creating a very simple oval with a bit of terrain)