DNS problems

I have a SBS 2003 Server PDC with 2 Windows 2003 BDC Server and a 1 Windows 2000 BDC Server. One of the Windows 2003 server is running a SQL Database which is connect from the clients to the Server via a ODBC connect. The SBS Server went down and none of the clients can connect. The DNS on all the clients is set to the PDC and also the ISP DNS Servers. The BDC’s all point to the PDC. I have tired to point all the clients to BDC but still can not connect. Can anyone help.