Somethimes is can happen, that when you try to access your blog at

http://yourhost/youblog/wp-admin

you end with a page showing 404 Error and in the url we see that we have been forwarded to

http://yourhost/youblog/wp-login.php?...

If you trace the logs of the server, what you will find is something similar to:

client denied by server configuration: wp-login.php

If this is the case - so most probably the problem comes from .htaccess file in your blog.

When you open it you will have something like:

<files wp-login.php>
  order deny,allow
  allow from 192.168.
  deny from all
</files>
#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

The problem comes from the third line - where “allow”-ed addresses to access login are registered. Check in the logs the IP address that you use to access wp-admin, or specify “All” if you want to be able to access admin from any place.

~Enjoy