404 error when I try to access admin panel

I installed a plugin called automatic upgrade and since then I can’t access my admin panel, the 404.php page is displayed instead. Here is what I tried to do to fix that (all these things didn’t work):

– checked in phpMyAdmin if the siteurl/home were the good ones
– looked if the index.php file was still in the wp-admin folder
– looked if the wp-login.php file was still at the root
– renamed the folder plugins into something else
– removed the files at the root, removed wp-admin and wp-includes and re-uploaded them all
– and of course removed the plugin I had installed

Any idea please?