Store in Production No Longer Works (can't fill carts or use Admin)

Hi,

I'm a consultant for a client who's had an e-commerce site in place since 2006. Their zen cart installation is no longer working. (You try to add items to a cart and it tells you your cart is empty.) Additionally they can't log in to the Admin page anymore. The original thing the client was complaining about was the fact that they'd let their SSL cert lapse (I installed a new one) and that they couldn't log into the Admin section. The fact that the carts won't fill was something I discovered separately.
Scouring the forums hasn't proven as helpful as I'd hoped.

This is hosted on DreamHost
PHP v5.2.14
Zen Cart v1.2.6
I don't believe there are any add-ons, I'm too new to zen cart to even know.
For that same reason I don't know in what ways (if any) customizations were made.
I've checked the forums and the FAQ and find similar problems and solutions but nothing that matches my experience 100% (and therefore not solving the problem.)

Questions and more info:

1. I can't find any chart or table that explains what the compatible PHP and Zen Cart combinations are supposed to be. I suspect DreamHost upgraded PHP along the way and perhaps that broke it? But how? In what way?

2. I am able to reset Admin account passwords (I can verify the tables change in MySQL) but when I actually try to log in as an admin user the software just dumps me back at the Admin login screen with no errors in the logs. I've read some of the proposed solutions (clearing cache and cookies) but that didn't change the behavior.

3. Someone else developed this site and if the solution is to upgrade the zen cart software to 1.3.9 I'm reluctant because I don't know if the original developer modified the code or not.

Someone please point me in the right direction.

Thanks!

c824

1. Zen Cart v1.2.6 was built with PHP 4 in mind. There could be many things in it that aren't compatible with PHP 5.2. It absolutely will not work on PHP 5.3.

2. The symptoms you describe are indicative of sessions not getting started properly. This could be caused by many things. Standard PHP session troubleshooting applies.

3. Upgrading from 1.2.6 to 1.3.9 is the best move to deal with this problem. Officially v1.2.6 is end-of-life and is no longer supported.
   To upgrade to v1.3.9 you'll essentially need to rebuild the template for the new version, redo any customizations, and install new versions of any addons used, if any.
   Then when you're ready to upgrade the actual database, the zc_install script will take the existing database and upgrade its structure to the new format and bring all the data forward to the new version, thus preserving all the existing data.

To identify what changes they made to their site vs original code, simply download a copy of the original code (see link on https://www.zen-cart.com home page, for prior versions), and then run a compare on the code using a tool like WinMerge. This is mentioned in the upgrade documentation. A summary of upgrade instructions is posted here: https://www.zen-cart.com/tutorials/index.php?article=98, along with links to more detailed instructions.