Active directory database is located in the directory :
c:\Windows\NTDS\ntds.dit
On Rare Situation this file can get damaged causing the hole active directory to malfunctioned including DNS and other services, Microsoft has some tolls to handle the situation and provide some tools to try and fix this database. To fix the ntds.dit database you first need to enter “Active directory Restore mode” by pressing F8 at boot :
Then open command prompt as Administrator, change to ‘c:\windows\ntds’ directory and run the repair command :
cd c:\windows\ntds ESENTUTL /p NTDS.DIT
ESENTUTL detect the page size automatically, Only if you have been told to you can use :
ESENTUTL /p NTDS.DIT /8
This will try to fix the database
Then you can check the integrity of the database with the G switch :
It will be good idea to delete/move the logs from that directory after the fix and before the restart
Good Luck