NOTE: This article links to important Facebook information on this subject.
Being unable to sign into your Facebook account blocks you from
messages, friends' updates and photos – but that's not always a bad
Since it's possible that another person could try to get into your
account and access your information, Facebook takes account security
very seriously. You don't want a stranger going through your messages,
posting status updates or changing the settings on your apps. The only
downside to this level of account safety is that sometimes you have to
take steps to access your account after a potential security threat.