A blank wp-admin page (no content, no error, sometimes a white rectangle where the dashboard should be) is a fatal PHP error that WordPress is suppressing instead of displaying. The dashboard uses more plugin and theme code than the public-facing site, so it's common to see the admin area break while the front end still loads fine. Turn on debug logging first to see the error, then isolate the plugin, theme, or memory limit causing it.
Turn on debug logging
Connect via FTP or the portal's file manager and open wp-config.php in your site's root. Find this line:
define('WP_DEBUG', false);
Change it to:
define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', true);
Save the file and reload /wp-admin. You'll either see the fatal error printed on the page, or find it in /wp-content/debug.log. The error names a file: a path under /wp-content/plugins/ means a plugin is at fault, a path under /wp-content/themes/ points to the theme. This is the same first step covered in fixing the WordPress white screen of death and fixing "there has been a critical error on this website", since a blank wp-admin is the same failure, just scoped to the admin side.
Turn WP_DEBUG_DISPLAY back to false once you've found the cause. Leaving raw PHP errors visible is a bad idea even in the admin area.
The three most likely causes
A plugin fatal on an admin-only hook
Some plugins only run certain code in wp-admin, so a bug there can leave the front end untouched while the dashboard dies. If FTP or file manager access works, rename /wp-content/plugins/ to /wp-content/plugins.bak/ and reload wp-admin. If it loads, rename the folder back and disable plugins one at a time until the blank page returns.
A theme function that only fires in the admin
Less common than a plugin fault, but a theme's functions.php can hook into admin-only actions and throw a fatal there while the public pages render normally. Rename your active theme's folder via FTP, for example /wp-content/themes/your-theme/ to /wp-content/themes/your-theme.bak/, so WordPress falls back to a default theme. If wp-admin comes back, the theme is the cause. The isolation logic here matches the plugin-versus-theme split used for the white screen of death.
PHP memory limit or version mismatch
The admin dashboard loads more scripts at once than most front-end pages, so it's more likely to hit a memory limit a theme or plugin doesn't hit elsewhere. If the debug log shows "Allowed memory size exhausted," raise the PHP memory limit in cPanel under Software → MultiPHP INI Editor, selecting your domain and increasing memory_limit.
If you recently changed PHP versions, an older plugin or theme may not support the new one. Go to Services → your hosting → PHP Version in the portal and roll back to the version the site ran on before. If the dashboard loads again, the plugin or theme needs an update before you move back up.
If none of that clears it
A blank wp-admin can also follow a botched database migration (see fixing WordPress database connection errors) or a corrupted .htaccess (related: fixing WordPress permalinks 404 on every page but home), though those usually affect the front end too. If the front end works but wp-admin stays blank even with all plugins deactivated and the default theme active, open a ticket rather than guessing further.
When to open a ticket
If debug logging shows a server-level error rather than a PHP one, if the site was working and broke with no changes on your end, or if you've isolated the cause but don't know how to fix the underlying code, open a ticket from the portal's Support section. A real person will look at the debug log and server-side logs with you, no phone tree involved.