Can't access local forum

[MarkHoward]

I have the following local directory structure:

htdocs

tab GeoKiwi
tab tab index.html

tab NZMotorhomeForum
tab tab index.php

When I point my browser at http://localhost/GeoKiwi the GeoKiwi index.html file is correctly opened
When I point my browser at http://localhost/NZMotorhomeForum all I get is blank white page.

I'd be grateful for some pointers on what might be wrong and where I can start checking.

Thanks