i had 2 win2003 server. first is PDC (DHCP+DNS configured) Primary Domain controller 2nd is ADC (Secondary Domain controller ) when pdc failed, i have to seized all fsmo roles using "ntdsutil.exe". now ADC is holding all fsmo roles. but DNS on ADC is not working. when i try to install & configure DNS on ADC, it gives message "unable to find root hints, that DNS already exists". i want to install and configure DNS on ADC and it will act as primary DNS. how to remove entries of previous DNS that are still present in Active Directory. can anyone guide me about this problem thanks

There is no PDC and BDC in an active directory domain. There is no "ADC" either. There are DC's...............period! I can tell from your use of NT 4.0 (and earlier) nomenclature (ie: PDC/BDC) that you don't really know much about 2003, Active Directory, or domain administration so I'm going to suggest you get some training or start using your computer to do research. Everything you need to know is freely available on microsoft's website and on other websites. The reason you are having so many troubles is that you don't know what you're doing. From what you've posted I would say your domain is toast and you're going to have to start from scratch. Take my advice, do some serious reading/research on Active Directory and Windows AD integrated domains before you start over. It may be possible to fix your issue by changing the DNS address on clients and ensuring that all DNS records point to the secondary DC but I suspect you're going to have to start over. In the future you might want to consider backups. They're a real big help when something breaks.