wp-admin not working

Hi,

I have 4 wordpress installations on one host which all have been working fine on 4 different domains.

Now today on one site I cannot get the wp-admin to come up when logged in.

I noticed the one site with the problem does not show the direct as normally on login, for example:

http://www.mysite.com/wp-login.php?redirect_to=http%3A%2F%2Fwww.mysite.com%2Fwp-admin%2F&reauth=1

I have not made any changes to this site lately. I deleted the .htaccess file and the wp-admin comes up. If i put the .htaccess file back the wp-admin screen is blank white.

The .htaccess is the same code on all four wordpress installations except for the domain name for redirect from non www.

Here is my .htaccess code which is the same on all installations.

# BEGIN WordPress

# Use PHP5 as default
AddHandler application/x-httpd-php5s .php
# mod_rewrite in use
RewriteEngine On
RewriteCond %{http_host} ^mysite.com [NC]
RewriteRule ^(.*)$ http://www.mysite.com/$1 [R=301,L] 

<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

Appreciate any help.

Gibs