Blizzard servers could not be reached or may be offline.
How to play Blizzard games in offline mode.
More information about authenticator security codes
What to do when getting an error that the Battle.net Account has logged in somewhere else.
Recovering a Battle.net Account when the email address has been forgotten
Some games require that you add a phone number to your Battle.net account
Instructions on linking your MLG and Blizzard accounts
Information about retrieving a locked account.