wp-admin redirects to 404

Question

Yesterday I logged onto my site and found that when I log in as an admin I get a 404 error as seen below:

I have done a bit of research and uploaded a backup, modified my .htaccess file to below:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

but to no avail.

Trying to access anything that is /wp-admin/ results in a 404 inclusive of the wp-stats image as seen in the picture.

I have downloaded a new version of Wordpress and uploaded it's wp-admin folder.

Aside from the above error, the site works fine.

EDIT

SHH Error log:

[Fri Apr 13 10:21:47 2012] [error] [client {redacted}] Premature end of script headers: index.php, referer: http://dailywealthreport.com.au/wp-login.php
[Fri Apr 13 10:21:50 2012] [error] [client {redacted}] Premature end of script headers: admin.php, referer: http://dailywealthreport.com.au/wp-admin/

Answer 1

One possible reason is that the /wp-admin has been reset to something else, for security reasons. The WP Better Security plugin can do this. I know, because I have in the past turned on a bunch of this plugin's options, without thinking too much about it, including the one that re-writes the /wp-admin URL so you need to go to /admin. -- And then I forgot about it too, which was frustrating!

Try moving all the plugins out of wp-content/plugins (to turn them off temporarily), then see if it works normally. Then, you can selectively re-turn-on the plugins and see what's going on.

Answer 2

Finding The Cause Of The WP-admin Redirection & Refresh Error

1. List item
2. Plugin Conflict
3. Theme Conflict
4. Reach Out To Your Web Hosting Support
5. .htaccess File Corruption
6. Site URL Error
7. Cookies And Cache

Answer 3

I was getting the same thing, tried everything from reinstalling WP, resetting my .htaccess and doing things that only made things worse. Turns out it I should have done was clear out my own Cookies And Cache. Problem fixed.