Do Not add SQL Server to the administrators group. That's a bad security practice, SQL does not need to be administrator and should not be administrator.

After granting the SQL Server service account locked pages permissions, you need to bounce the service (not the server). If you don't have rights to do that permission assignment, ask your AD administrator to set up the correct OUs in Active Directory, add the SQL Server servers to that OU and set up the GPO to assign the required permissions.