I think there are a couple of things we can try.
The first is to clear any and all old cookies lurking about in your browser. Clear all AFF cookies from your browser’s history and cache, and then close the browser to make sure those changes actually happen. AFF will reset cookies for you, and the subdomains actually require a reset every month in the form of confirming you are over 18.
The second thing is your password. Somewhere between your last login and now, we changed the way passwords work. Passwords need to be between 8-12 letters and/or numbers long, with no special characters, and they are, as always, case sensitive. Additionally, if you reset your password using the existing password, it blanks the field and forces a reset yet again. So, once you’ve eliminated the potential issue of old or currupt cookie strings, this would be the next thing to check, to make sure your password actually fits the requirements.
You should see the Login option as an item at the end of the menu bar. It’s a dropdown, and you need to input your email address and password, and then click the login button. The Login item at the end of the menu bar should now show your pen name if login was successful.
If these steps don’t help, let me know and we’ll see what else it could be.