THAT was an ordeal.
For whatever reason, my WordPress installation decided to send all Admin Logins to a 404 error. I did a WACK of Googling, and was only able to log back in after renaming the .htaccess to .htaccess.old . Deleting it could work too.
I tried disabling plugins.
I tried restoring a site backup.
I tried restoring a database backup.
I tried earlier versions of both.
I contacted my web host, to no avail.
So, when your wordpress admin login gives a 404 error – delete this .htaccess file.
Of course, this might be the only time I get in, so….