Step 1: Is the admin also down?

Try yourdomain.com/wp-admin. If the admin opens, deactivate the plugin you last installed/updated (Plugins → Deactivate) — that's the most common single cause.

Step 2: Disable all plugins via File Manager

1. cPanel → File Manager → open public_html → wp-content.
2. Rename the "plugins" folder to "plugins-off". This disables every plugin at once (nothing is deleted).
3. Reload the site. If it works, a plugin is the culprit: rename the folder back to "plugins", then rename/activate plugins one by one until the error returns — that's the faulty one. Delete it and find an alternative.

Step 3: Rule out the theme

1. In wp-content → themes, rename your active theme's folder.
2. WordPress falls back to a default theme if one is installed. If the site loads, your theme (or its latest update) is the problem — reinstall a fresh copy or contact its developer.

Step 4: Raise the PHP memory limit

A white screen right after installing something heavy can be memory. Raise memory_limit via cPanel → Select PHP Version → Options (see "How to Increase PHP Limits") and reload.

Step 5: See the actual error

1. In File Manager, edit wp-config.php in public_html and temporarily set the WP_DEBUG line to true: define('WP_DEBUG', true);
2. Reload the site — the error message names the file and plugin/theme involved.
3. Set it back to false when finished — a live site should never display errors to visitors.