How do I go about fixing this apparently messed up upgrade?

I’m a WordPress novice trying to help a friend (who is even more of a WordPress novice) with his WordPress blog hosted on GoDaddy.

It was working fine until he apparently (he doesn’t fully remember) was prompted to upgrade the software.

Now the blog still works for end-users (you can see it here) but whenever you log into the WordPress admin, you get a Page Not Found / “This is somewhat embarrassing, isn’t it?” page. The URL that the browser has been redirected to is: http://brewstersmith.com/wp-admin/upgrade.php?_wp_http_referer=%2Fwp-admin%2F

It seems like the upgrade attempt was messed up somehow. Given I don’t know what precisely caused this, what steps should I take to start investigating the problem and ideally rolling back the upgrade (or completing it) so that the blog is usable again?

The first thing to try:

1. Manually download a fresh copy of WordPress
2. Log into the FTP account and upload everything EXCEPT the wp-content folder

It is important that you do NOT copy over the wp-content folder or the wp-config.php files. These are custom to each site.

This will allow you to make sure the upgrade is complete.

If that doesn’t work, you should remove the .htaccess file from the site, and see if you can get access back to the admin.

Also… Godaddy is on my short list of hosts that I won’t work with on WordPress sites, but it does generally work with very basic site setups.