In the subdomain folder, find or create a file named .htaccess
Add or make sure you have the two lines:
Code:
Options All -Indexes
DirectoryIndex index.html
The first prevents the listing of the contents.
The second tells Apache to serve up index.html as the default page. You can add more names
Code:
DirectoryIndex index.html index.php default.html home.php
and Apache (the webserver) will pick the first match as the default page.
Edit:
also Index.html is not the same as index.html
Capitalization matters on *nix computers.
Why this happened:
You probably have a .htaccess file in your root directory that sets the default page to index.php or something similar. The subdirectory inherits that directive. Putting a .htaccess file in the subdirectory overrides that.