Toolbar not showing and wp-admin showing blank page ?

Please, do not edit core files under any circumstances.

Re-upload the entire WP core installation, overwriting any existing files, to ensure that you changes are completely removed. This should resolve the issue, assuming it’s related to the changes you made.

If not, check the PHP error log to see what file/function is causing a PHP fatal error.

You can also try temporarily disabling all plugins via FTP to see if the error is caused by an active plugin. You can either rename the wp-admin/plugins/ folder, or move the individual plugin folders to a new hidden sub-folder (ie. wp-admin/plugins/.inactive/) to disable plugins via FTP. They will still be “active” plugins as far as WordPress is concerned, but WordPress will not be able to load them, so they will not executed. Warning: If you visit the Plugins page in the admin while one or more plugins are deactivated in this way, WordPress will throw a warning and deactivate these plugins until you move them back and re-activate via the admin dashboard.