Server 2003 not allowing to join Workstation after configuring ADS?

I have already a Domain but trying to install one new Server. I have installed Windows Server 2003 and install Anti virus while its resources were accessible from other Workgroup Computers and from old Server Clients Machines, but when i install Active Directory in it using same IP table but with another Switch, its resources are not been accessible from any computer while ping is completely running(from ip and from DNS name). I have also seen that it is not allowing to join Clients Computers to the server. Can some body help regarding this?