I'm having trouble logging in with my username and password

If you're repeatedly prompted for your username and password, or if you're getting an 'invalid credentials' or 'web login required' error, make sure your password is correct. Keep in mind that password are case-sensitive.

If you’re sure your password is correct, sign in to your account from the web version of Gmail instead at http://mail.google.com

In most cases signing in from the web should resolve the issue, but you may also want to try these troubleshooting tips: