Most WordPress errors fall into 5 buckets. Here's the fix for each.
White screen of death (WSOD)
Almost always a plugin or theme. Connect via FTP, rename wp-content/plugins to plugins-off — the site comes back. Rename it back, then deactivate plugins one at a time to find the culprit.
"Error establishing a database connection"
- Check the database credentials in
wp-config.php— they must match cPanel. - If they look right, your database user may have lost privileges. cPanel → MySQL Databases → re-add the user with ALL PRIVILEGES.
- If the database server is down, you'll see this on every site at once — open a ticket.
HTTP 500 / "Internal Server Error"
Check error_log in your public_html folder — the actual error is in there. Common causes:
- A broken
.htaccess— rename it to.htaccess.old, then in WP admin go to Settings → Permalinks → Save to regenerate. - A PHP memory limit hit — add this to
wp-config.php:define('WP_MEMORY_LIMIT', '256M');
"There has been a critical error on this website"
Check the email WordPress sends to your admin address — it includes the exact plugin and file that caused the crash. Disable that plugin via FTP.
Stuck in maintenance mode
An update was interrupted. FTP into the site root and delete the file called .maintenance.