Kevin... in your post #11...
/includes/languages/english/html_includes/define_main_page.php
... is the file that is rendering the content showing on the site.
and...
/includes/languages/english/html_includes/classic/define_main_page.php
... was NOT rendering its content.
(Though I see now that you have a template called denim).
even so...
Zencart's OVERRIDE system works this way.
-
it will look FIRST for a file in an over-ride folder. IF it finds a file that is OK, it will use that file.
-
If it does not find the file it needs in a valid over-ride folder, it will go fetch the CORE (default) file.
In your case, number "2" seems to be happening, suggesting either:
a) a corrupted /missing file at: /includes/languages/english/html_includes/define_main_page.php
b) a mis-named over-ride folder
If you load a fresh define_main_page.php file (from a download of ZC software - use the DEFAULT file) into your includes/languages/english/html_includes/denim folder... what happens?
The point is that zencart works this way... if it is not showing the file in the over-ride area, then it is simply reverting to the default file.
You need to address WHY it is not seeing the over-ride file, and that's usually a case of badly edited PHP code, a missing or mis-naled file, or a file in the wrong location.
IE: it can only be an error caused by a person - not the software.