Goodday

OS: 2000 advance server
Please Help
Active Directory not working.
Every Time i dbl click on ACtive Directory Users and Computers
It pop up this error message

" Naming Inofrmation cannot be loacted because:
The specified domain either does not exist ir could not be contacted. Contact your system administrator
to verify that your domain is properly configured and is currently online."

Please help.
AD used to be working fine.

Please explain in detail. I not so familiar with staff from adminstrative tools