PrestaShop, the 500 error and demo mode, how to restore the store
A PrestaShop store can stall in two confusing ways: a full 500 error, after which the page does not load at all, or demo mode, where the store works but you cannot save any change. Both look alarming, and both can usually be fixed without losing orders. Let us go through them in turn.
The 500 error in PrestaShop, where it comes from
A 500 error (Internal Server Error) is a server message that says only "something went wrong", without saying what. The most common causes in PrestaShop are:
- A corrupted .htaccess file (often after changing URL settings or installing a module).
- An exhausted PHP memory limit on a larger store or with a heavy module.
- A module conflict or error, especially after an update.
- A PHP version change on the host that an older PrestaShop or module does not work with.
How to find the cause: debug mode
Instead of guessing, enable developer mode. In the config/defines.inc.php file find the line with _PS_MODE_DEV_ and set it to true. Instead of a white page you will see a specific message with the name of the file and module that triggered the error. It is the fastest route to the heart of it. After the diagnosis, be sure to turn dev mode off, because on a live store it reveals sensitive details.
Also check the server logs in your hosting panel, with a 500 the answer is often right there. If instead of a 500 you see a blank white page, we cover it separately in the post on the white screen in PrestaShop.
Demo mode, or "I cannot save changes"
A completely different symptom: the store works, but when you try to save a setting, a product or a module you get a message that changes are blocked. That is demo (demonstration) mode, a safeguard used on demo stores so visitors do not break the configuration. If it turned on by accident (or a previous contractor left it on), you disable it in the panel under advanced settings. Once off, saving returns to normal.
Before you start: a backup
Whatever you change in the files or store configuration, first make a backup of the files and database. In a store, orders and customer data are at stake, so a safety net matters here more than anywhere else.
When the store is down and orders are waiting
With a store, every hour of downtime is real lost orders, so long experiments on the live version rarely pay off. We handle PrestaShop store repair: we diagnose for free, work on a copy, and restore the store without the risk of the order history disappearing. Get in touch if you want us to take care of it.