|If you were logging in and only using the default Administrator account, then when you create new accounts the default administrator no longer shows up.|
You can access it by, at the welcome screen, do a couple of control-alt-delete to bring up the logon box where you type in administrator and its password.
There is also a tweek to have it show up on the welcome screen but I forget what it was. Should be easy to find via a web search.
Concerning the files they are not lost but still there. You can logon as the original administrator and copy them to the new user admin profile or under the new admin account take ownership of them [not what I would recommend].
For more info google taking ownership of files.