If you're having trouble logging in, it may be because you've saved your passwords to your browser.
You can still find those easily. Just go to your browser's preferences (usually through the menu on the far right of the toolbar that looks like this ≡ ) and choose your saved passwords (in firefox, it's under the security settings).
You can search for pottersarmy.net (yep, the old domain) and then check the show passwords checkbox. A popup will appear asking whether you're sure. Yes you're sure.
Then write down all your characters' passwords.
As a note, saving passwords to your browser is a security risk. Security experts say you're better off writing them in a physical notebook because it's unlikely anyone is going to break into your house just to find your site passwords.
If you still can't log into your character after this, please post in the help forum letting us know. It's guest friendly, so you can post there without logging in. We'll reset your password and you'll get an email letting you know.
If you've used a fake email for your character, we can't reset your password. Basically, we have no way to confirm that the person posting in the help forum is really you. You'll have to make a new account for that character. ¯\_(ツ)_/¯