Microsoft has written Knowledge Base article Q260371 - Troubleshooting Common Active Directory Setup Issues in Windows 2000.
I quote the beginning of the article, which you should read in its' entirety:
"Some common issues that you may encounter with Active Directory installation and configuration can cause a partial or complete loss of functionality in Active Directory. These issues may include, but not be limited to:
Domain Name System (DNS) configuration errors
Network configuration problems
Difficulties when you upgrade from Microsoft Windows NT
This article describes how to troubleshoot Active Directory issues by identifying common configuration issues. For more information about any of the issues described in this article, consult the Help system in Windows 2000, and the Deployment Planning Guide, which is located on the following Microsoft Web site:
Chapter 9 of the Deployment Planning Guide describes the design of the Active Directory structure, which is essential to a successful Windows 2000 Active Directory deployment. Chapter 9 of the Deployment Planning Guide is available on the Internet at the following Microsoft Web site: