While upgrading WordPress to the latest version, 3.4.2, we faced an issue, we were not able to see the admin pages. It was throwing an 404 error (page not found). There were no plugins installed and the theme which we had created was very straight forward. We had never faced any such problems earlier with WordPress. All the upgrades used to be very smooth. We have hosted our sites on godaddy.
We went on digging the issue. had a chat with godaddy team, and figured out that the issues is not with them. They gave the solution.
This wordpress update script is buggy (chances are 1 out 10 ), It doesn’t the update the database number properly. So we have to update the file manually. The file which needs edit is inside the wp-includes folder, version.php. So using FTP you need to edit that file, and change the database number. You can find the database number in your database wp_options table, look out for db_version.
hope this helps…