Regedit:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList

Locate the correct user with S-1-5 (SID key) followed by a long number.

If listed twice, once with .bak, then switch the names.
If listed once remove the .bak.

Change the RefCount value to 0
Change the State value to 0

Reboot.

Source: Microsoft