Unfortunately the problem you have is unrelated to Admin Tools. You have accidentally unpublished the back-end login module from Extensions, Plugins at the back-end of your site. This is something which Admin Tools cannot possibly do to your site. You did it by accident. We can try to help you but please do note that this is outside the scope of our support.
Solution: Using phpMyAdmin -or whatever your host is providing to edit your database- edit the #__modules tables of your site. Find the row with id = 2 and set the published value back to 1 (it should be 0 right now). This will re-enable the login form on the back-end of your site.
Note: You will need to replace #__ with the common database table name prefix, i.e. the common part up to and including the underscore your site's tables are using. If you are not sure what it is open the configuration.php file of your site and look for public $dbprefix in it. The value between the backticks is the prefix.
Nicholas K. Dionysopoulos
Lead Developer and Director
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