One of my relatives tried to log in to his Facebook account and was greeted with the message that his account had been disabled. There are no notification emails in the email account associated with his Facebook.
There are a lot of reasons this could happen, but it happened to my wife's Facebook account about a month ago because someone hacked her account (Facebook detected someone logged into her account from Nigeria).
I am unable to access Facebook right now, but under the "Help" section on Facebook, we were able to find a link that explained how to submit a ticket to the Facebook team to resolve the issue. They got back to us and asked us some security questions (like what was the last item you posted on your FB account, etc.) and they re-activated it for her. (It took about 5 days though)
Just search the Facebook help section for "disabled" and you should find it - I googled for it, and found this page, which may or may not help (I don't have access to that page right now).