Some primary reasons for this are listed below-  The account of the system administrator is disabled   The Windows Groups included in the sysadmin fixed server role may have got deleted by mistake.  The password of the system administrator account is incorrect  The login credentials of the sysadmin fixed server role members are removed by mistake.  The logins of the sysadmin fixed server role members may have been assigned to people who may have left the organization or are not available for some reason or other.