I just moved the DNS record for a site over that was forwarding to a wordpress installation. When I did the root domain for the Wordpress install was compromised and the pages of the site no longer worked.
The next thing I did was login and goto settings>general
You'll need to update the domain to the new root domain.
I started getting 500 ErrorDocument errors. The problem was that the .htaccess file was incorrect and needed to be updated. I renamed the existing htaccess file in order to keep from losing it just in case I needed it.
Inside the Wordpress Admin Goto Settings > Permalinks and once there save the settings ; it will republish the htaccess file