Proxy

I am the Network Admin at a school. I currently have a PDC running in the office and a BDC running in the computer lab. I also have a Proxy server set up as a stand alone. All systems are running NT4.0 and Service Pack 6a.

Here is my question. Weare currently in the summer months and there is no school. I wanted to take the BCD off line to upgrade, however once the BDC was taken off line no one was able to log on to the net work from the office. No one was able to access the proxy server. The error is “there is no domain controller to validate your password”. Why is the PDC not validating? From what I was to understand if either the BDC or PDC went down the other should fill in. Any help would be nice.