I have a website that has been down for awhile with the redirect loop. I also cannot access wp-admin, gives me the same exact message. I was wondering if i could get this fixed asap since its a customers website. Thanks!
Did you update the WordPress Address (URL) and Site Address (URL) in the database or back-office ? Does it match with your
wp-config.php WP_HOME and WP_SITEURL. If it still doesn't work you can deactivate all the plugins (rename the
wp-content/plugins/ folder) and reinstall them one at a time.
Source : WPBeginner