Can only suggest

1)Usernames and passwords are case sensitive!

2)Try a reboot of your server!,

3)If using "chrome" try that!

4)If you have access to the data base ie phpgpadmin , see "res_user" for "usernames" and "passwords" just to check

David Dean just answered this on another question in this forum: https://www.odoo.com/forum/help-1/question/how-can-i-log-back-in-to-odoo-with-the-administrator-account-odoo-asking-for-admin-email-instead-of-username-59663

Put "admin" as the Email address (no @ symbol or anything else). 

Use the password you set up when you created the database.

You are logged back in!  

David mentioned that Email and Username are synonymous - you don't have to use an actual email address as the username even though the field is labeled "Email".

It looks like you have issues with logging in (#4).

Username: admin password: the password you specified when you made the database (step 2). It is not admin, but the password you typed in twice.

I'm running into the same problem and when I look in my database for the admin password I find this: login | password
-------+----------
 admin |
(1 row)

no password?

So,

1) I realize that usernames and passwords are case sensitive.

2) If by restarting the computer I have effectively restarted the server as well, then I have tried that. If I am mistaken, what did you mean?

3) I will try Google Chrome.

4) The database should be installed on my computer. How do I access "res_user" to check the usernames and passwords?

I noticed that when I go to the localhost:8069/# screen in Firefox I can go to "Backup" and I see that the proper database name is there and that it asks for the admin master password which I have not changed from the original "admin".

I'm still confused.

Thank you.