This happens when PHP memory limit is exceeded or a plugin conflict occurs. Open your wp-config.php file via FTP and add this line before 'That's all, stop editing!': define('WP_MEMORY_LIMIT', '256M'); If that doesn't help, rename your plugins folder through FTP to plugins_old. This deactivates all plugins at once. Try accessing your site again. If it works, rename the folder back and deactivate plugins one by one to find the culprit.
The White Screen of Death usually means a PHP error. Enable debug mode by editing wp-config.php. Find define('WP_DEBUG', false); and change false to true. Refresh your site and check the error message. Most often it points to a faulty theme or plugin. Switch to a default WordPress theme by renaming your current theme folder via FTP. This forces WordPress to use a fallback theme.
Disable unnecessary widgets from Screen Options at the top right of your dashboard. Remove external RSS feeds and complex widgets. Check if your database needs optimization. Install WP-Optimize plugin or run OPTIMIZE TABLE command through phpMyAdmin. Hosting resources might be insufficient for your traffic level. Contact your provider to verify CPU and RAM allocation.