Wordpress - I'm getting a 404 message when I try to access wpadmin

Delete .htaccess

type in domain.com/wp-login.php

login.

Dashboard -> Settings -> Permalinks -> Save. (just automatically recreates your .htaccess again).

If the problem persists. Try disabling plugins. Enable plugins 1 by 1 until the problem occurs again. That will narrow down the faulty plugin.