do you have a dedi or vps or are you on a shared?

If you have default .htaccess file in the root of the software, then something is wrong with the mod_rewrite module on your server. 

Make sure you have .htaccess file and it has default content, if it does, contact your hosting provider to configure mod_rewrite properly. 

Also what do you have as your home_uri in the ow_includes/config.php file?