Can't log in to admin site in Django
I think you should try these step:

create new admin user 
python manage.py createsuperuser 
use new account log in admin site
reset password for your account and remeber it 
log in admin site with your original account
I was working through the polls tutorial and everything was fine until I tried to log in to the admin site; it just said 

"Please enter the correct username and password for a staff account. Note that both fields may be case-sensitive."

So I Googled the issue and tried everything I could. Here are all the problems I investigated:

Database not synced: I synced it and nothing changed.
No django_session table: I checked; it's there.
Problematic settings: The only change I made to the settings was the addition of'polls.apps.PollsConfig', to INSTALLED_APPS.
User not configured correctly: is_staff, is_superuser, and is_active are all True.
Old sessions: I checked the django_session table and it's empty.
Oversized message cookie: I checked and I don't even have one.
Created superuser while running web server: I did this, but after stopping the web server, creating a new user, and restarting the web server, and trying to log in with the new user, it still didn't work.
Missing or wrong URL pattern: Currently I have url(r"^admin/", admin.site.urls) in mysite/urls.py.
Entering wrong username: The username I created was "admin" and that's the same one I'm typing in.
Wrong server command: I'm using python manage.py runserver.
Something wrong with database: I tried deleting the database and then reapplying the migrations, but nothing changed.

Is there anything I haven't tried yet, or am I missing something?