Navigate the the location below in your registry and make the corresponding change.

Create or edit the existing DWORD value named 'DisableDefaultPasswords', and change the value to '1' to disable automatic logon, or '0' to automatically logon. 

Key:[HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\NWNP32\NetworkProvider]
Value Name: DisableDefaultPasswords
Data Type: REG_DWORD