Strange page-not-displaying issue

[liquidhorse]

Hi, I am a new to ZenCart but experienced Linux admin. I set up a test cart to play around with the system, and everything runs fine until my test user attempts to create either a new account, or to complete the checkout. In both cases, the system attempts to browse to some particular page (respective to the action), and simply does not respond. In the case of the checkout completion, refreshing the page resubmits the order (verified in the admin tools). This happens both with a relatively vanilla site and the demo site that comes with the install. The URL addendum, for checkout, reads: /index.php?main_page=checkout_process

I am using the very latest release of ZenCart. I am running PHP 5.2.3 and MySQL 5.0.33, which I understand could present some issues. However, so far I have not noticed any actual database issues - even operating the cache in file-mode (as opposed to database-mode) produces the same results. Also, the apache error logs have no useful info - the access log shows a request for the page, but no errors are generated...and neither are the pages! All other pages seem to work fine...

I tested on both Linux and Windows systems, with Firefox and Explorer - the same thing happens everywhere.

If anyone is interested in seeing (hopefully) this issue in action, let me know and I will point you to the right place!

Thanks!!!
...matt

[liquidhorse]

UPDATE: After installing XAMPP and playing around with zen-cart in php4, I received the following message on the two pages that came up blank on my prior installations:

Email Error: Could not instantiate mail function.

I don't have sendmail installed, which is likely why things are going awry. Sorry for the trouble... I do not know why php5 did not display the message.