Found this: at this page
: 1. A user profile exists in the storage but it has disappeared.
In some cases, the profile exists in the hard disk but it just does not appear at the Welcome screen or in the User Accounts
folder in the Control Panel. In such cases, the user may receive the following error message when he/ she attempts to create a new account with the same name; “the account already exists”. This happens when the user account has been disabled or is not active. Such accounts do not appear in the User Accounts or at the Welcome Screen. These disabled accounts can only be accessed in the Local Users and Groups window. To determine whether an account is active or not, follow this:
a. Go to RUN, type in “compmgmt.msc”, hit Enter.
b. Double-click on the Local Users and Groups folder.
c. Double-click on Users.
If a user name is displayed with a red cross in the check box before it, this means that the account is disabled or not active. In order to activate the disabled user account:
a. Double-click the user name.
b. Unclear the ticked check box.
This way, the disappeared profile will show up again at the Welcome Screen as well as in the User Accounts folder in Control Panel.
Read more: http://www.brighthub.com/computing/windows-platform/articles/33588.aspx#ixzz1AJ9HCaCA