Some users decide to close or deactivate their Facebook accounts when they get tired of the social networking site. Facebook automatically stores the data for closed and deactivated accounts so that users can reopen them again easily if they have a change of heart. If you previously closed or deactivated your Facebook account but now want to reopen it, you can easily reactivate the account by logging in with your old username and password.
Launch your Web browser, and navigate to Facebook.com.
Type your username into the relevant input field on the Facebook login page. The username is the email address that you used when you first registered the account.
Type your password into the relevant input field. Enter the password carefully, because Facebook uses case-sensitive passwords.
Click the "Login" button. This will open and reactivate your Facebook account. You can access your Facebook friends list and all previously uploaded data, including status updates, notes, photos and videos.
If you’ve forgotten your Facebook password, then you can reset the password by clicking the “Forgot My Password” link from the login page. Once you’ve answered the security questions in the on-screen dialog box, Facebook will email you with a new password so that you can sign in to the account and reactivate it.
You might not be able to reactivate your account if it was disabled by Facebook for security reasons or for breaching terms and conditions.