Nevertheless, the 404 comes from the origin, therefrom if /wp-login.php or wp-admin/ doesn’t load and work as expected, I am afraid you’d have to start troubleshooting by renaming the plugins/ folder to plugins-test/ and see which plugin might cause such case or interfere with WordPress defaults. Might be some Security plugin, or Hide my WP, or Change wp-login, some Maintenance plugin?, etc.
If not, then cross-check your web server configuration files and your .htaccess as well.