If you do not want users to be authenticated before using the system then you can make use of this trick. Note that for Windows with multiple users it is not recommended to disable the start up login dialog box.This will affect privacy.
Open the run dialog (start > run).
Type "Control Userpasswords2" without quotes and click ok.
In the resulting User Accounts dialog box, uncheck the "Users must enter a user name and password to use this computer" check box.
Click the apply button.