I put together a site: abrahamlincolnbiography.org
The WordPress installation is at abrahamlincolnbiography.org/media/wp-admin in the media subfolder. My htaccess reflects the subfolder, as does the index.php file from WordPress placed in root. I don't think the issue is to do with the subfolder as I've setup dozens that way before.
Anyway, a week ago I got a 404 error, 'Nothing found for...' going to the administration. Before this point I had no problems getting to wp-admin.
I've also tried removing plugins and reinstalling WordPress to no avail.