Terrain modeling - Incomplete!

[Anonymous]

Hi all.

I'm doing some terrain modelling of the site and surroundings of a hotel I'm working on. I've donde the process a few times before and worked fine but this time I don't know what's happening.
Steps are, attach survey dwg, then create the mesh, then with the magic wand I add the contour lines to the mesh, and then I input a new height for each contour line as per the survey. It seems to work fine, the line are changing in height, only the mesh seems to be sliced horizontally with the upper half not showing at all.
An image is worth a thousand words so please see attached and thanks in advance for any help.

[Anonymous]

First image is of the resulting mesh while selected, you can see the contour lines actually have changed height. Attached is the image of the unselected mesh where you can see more clearly how it is "sliced" and upper part is invisible.
Any ideas?

Thank you.