to reset your Default Domain Policy and/or Default Domain Controllers Policy GPO to their default settings, perform the following steps:

1. Log on as a Domain Administrator to a Domain Controller.
2. Open an elevated command prompt.
3. Enter the parameter to reset:
   • dcgpofix /target:Domain to reset the Domain GPO.
   • dcgpofix /target:DC to reset the Default DC GPO.
   • dcgpofix /target:both to reset both the Domain and Default DC GPOs.
4. After you enter the appropriate command in Step 3, enter Y to both prompts.
5. Close the command window.

For additional information on the dcgpofix command, refer to the Microsoft Technet website.

Though not as widespread, problems can occur if you have edited a machine’s Local Security Policy. This policy can also be reset to its default settings with the following steps:

1. Log into an account with local administrative rights on the machine in question.
2. Click Start, Run, then enter “cmd” in the prompt, then <Enter> to start a command session.
3. Enter secedit /configure /cfg %windir%\inf\defltbase.inf /db defltbase.sdb /verbose to reset Local Security Policy.
   
   Source: Microsoft Tech