White screen at checkout

I have zen cart 1.3.8 running here, http://www.ccowaterfowl.com/store2. Until recently everything has been working fine, and now clicking the checkout button goes to a blank screen.

To get it to get to that point I also had to disable 2 products. Prior to those two products being disabled adding an item to the shopping cart or viewing the shopping cart would cause the same problem.

I followed instructions I found here on the forum to make zen cart show the php error messages, and there are none that seem relevant, or at least they show up on every page, not just pages that don't work for whatever reason.

Any help would be greatly appreciated.

If you are getting PHP error messages then you need to sort them out. Ignoring them isn't an option. Nor can we help you if you don't tell us what they are.

This is what I just got trying to add an item to the cart, along with a white page that is.

Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at /hermes/web01/b1388/pow.tomfaulkner/htdocs/customers/ccowaterfowl.com/htdocs/store2/index.php:2) in /hermes/web01/b1388/pow.tomfaulkner/htdocs/customers/ccowaterfowl.com/htdocs/store2/includes/functions/sessions.php  on line 109

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /hermes/web01/b1388/pow.tomfaulkner/htdocs/customers/ccowaterfowl.com/htdocs/store2/index.php:2) in /hermes/web01/b1388/pow.tomfaulkner/htdocs/customers/ccowaterfowl.com/htdocs/store2/includes/functions/sessions.php on line 109

Notice: Constant OFFICE_IP_TO_HOST_ADDRESS already defined in /hermes/web01/b1388/pow.tomfaulkner/htdocs/customers/ccowaterfowl.com/htdocs/store2/includes/languages/english/email_extras.php on line 53

Warning: Cannot modify header information - headers already sent by (output started at /hermes/web01/b1388/pow.tomfaulkner/htdocs/customers/ccowaterfowl.com/htdocs/store2/index.php:2) in /hermes/web01/b1388/pow.tomfaulkner/htdocs/customers/ccowaterfowl.com/htdocs/store2/includes/init_includes/init_templates.php on line 79

Warning: Cannot modify header information - headers already sent by (output started at /hermes/web01/b1388/pow.tomfaulkner/htdocs/customers/ccowaterfowl.com/htdocs/store2/index.php:2) in /hermes/web01/b1388/pow.tomfaulkner/htdocs/customers/ccowaterfowl.com/htdocs/store2/includes/functions/functions_general.php on line 45

I have errors showing at the moment, so everyone browsing can see them.

I should add that this was working before and no php/html files have been changed on the server. The only files that I think have been changed have been product images.