Logon failure on domain controller

My BDC-windows 2000 server--will not permit any user to authenticate. The Event log shows Logon Failure for every attempt. Also, even when using my admin logon, I cannot access the controller from the "explore" screens because "the target account name is incorrect." But if I use the full UNC I can map a drive and access the server.
The controller shows Event ID: 675, 676 and various failure codes. I have checked kerberos, WINS and replication and can find nothing amiss.