Can’t login after running WordPress Automatic Upgrade

Today I ran the WordPress Automatic Upgrade plugin on my travel blog, but when I wanted to upgrade the database, as requested, it wouldn’t let me login. I didn’t get a password error, it just reloaded the login page.

I tried resetting the password, but didn’t receive an email. Then I saved the mysql database and did a clean WP install – but as soon as I re-import the mysql database, the same thing happens again. I also tried changing the password in phpMyAdmin, but it still just reloads the login page.

My blog appears to be empty, as you can see, although you can still see the number of posts in the category navigation in the sidebar.

I’d be ever so grateful if someone could come up with a way to fix this issue, short of copypasting every single post from the mysql dump – those are several years of my travels… Thanks for your time!