Disable the "Log on using dial-up connection" Check Box

Start/Run/Regedit
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon. Value Name: RasDisable, Data Type: REG_SZ (String Value), Value Data: (0 = restriction disabled, 1 = restriction enabled). Create a new String value, or modify the existing value, called 'RasDisable' and edit the value according to the settings below. Exit your registry, you may need to restart or log out of Windows for the change to take effect.