I have managed http://www.maxedisplay.co.uk/ for nearly a year now and the boss wanted to change the look. Original store started life as a slightly modified version of an algozone.com template but the text heavy and the postage stamp (as my boss called it), Categories on main page design was to be replaced by a simpler graphical centre menu with big graphics.
I have attempted to use html table with images and links inserted into the define_main_page.php that previously just held the introduction text to achieve this. This meant that the Categories - Always Show on Main Page from Layout Settings could be turned off as that grid was to be replaced by the new table. Here is where the problem arose, everything in the middle column just disappeared. Checked what I'd done and couldn't see problem with this modification. Suspecting the template code may be to blame I tried the same process with Original Green instead and it works fine.
I know your gonna say "talk to Algozone", but they limit to support to the first month or so and not on user modified sites.
In summary : define_main_page.php shows up if Categories - Always Show on Main Page is set to 1 or if the Original Green Template is used. If the Algozone template is used and the Show on Main Page is 1 it works, but with Selected Category displaying below (my work around for now, with low level category selected), if set to 0 everything totally disappears in the middle column.
Has anyone any idea what would make this happen, which php files could effect this? I will put up some code if you specify what you need to look at, the problem area code ie. when its broken isn't very interesting just a hole.
<!-- content //-->
<td width="100%" valign="top" class="maincont_mid_td">
<div class="centerColumn" id="indexDefault">
<div id="indexDefaultMainContent" class="content"></div>
<!-- bof: specials -->
<!-- eof: specials -->
<!-- bof: featured products -->
<!-- eof: featured products -->
</div></td>
<!-- content_eof //-->



