W2Kcreated new user account on same user

On a Windows 2000 stand alone machine, when the logged on, suddenly all his regular desktop shortcuts and the content of the startmenu folder had changed – e-mail accounts gone etc.

Looking under “Documents and Settings”, i discovered, that his username apeard twice as:

[Username]
and
[Username.pc-name]

I found all his regular shortcuts etc. under the first folder [Username], but for some reason, the account had been “recreated”, and when he now types in his regular logon, the PC chooses [Username.pc-name].

How do I change this back?
..Will it for instants work, just to Copy the content of [Username] into [Username.pc-name]?

(And for kicks: How does this thing happen to begin with?)

Thanks in advance for any responce.

Borgesen, Denmark