Control Panel/Users/Change the Way Users Logon/Welcome Screen or…

Start/Run/Regedit Key
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\ CurrentVersion\Winlogon]
Value Name: LogonType Data Type: REG_DWORD (DWORD Value) Value Data: (0 = Classic Mode, 1 = Welcome Screen) Create a new DWORD value, or modify the existing value, called ‘LogonType’ and edit the value according to the
settings below. Reboot.

Or

Download the INF fix here.  To use: Download the xp_admin_enable.inf file (you may want to right click and use Save Target As).  Locate the file you downloaded and right click on it, then select Install.  Or Download the VBS Fix here.  To use: Download the xp_admin_enable.vbs file and save it to your hard drive (you may want to right click and use Save Target As). Double-click the xp_admin_enable.vbs file. You will be prompted when the script is done. INF and VBS files can be viewed in Notepad.

Source : Kellys-Korner