30+ computers suddenly got froze and disconnected from network

[Jan Shu]

Hi All,

A week ago, one of our WAN T1 cables was cut by a local phone company. This caused some connection issue between our offices. During the troubleshooting, the network admins and system admins possibly had done some changes on our Cisco router/switches/firewall or the W2K Active Director Domain Controllers. Now the phone company has fixed the WAN cable, but we got new problem in several US offices which have either LAN or VPN connections. For 6 days, 50 - 100 computers (total 1000+ computers) suddenly got froze/hung and disconnected from network all within 1-5 minutes and repeated several times a day. When the computers froze, only the mouse cursor could move, nothing else would respond, and computers were disconnected from domain network immediately. And the computer CPU processors became 90%+ busy. It happened on W2K, W2K3 servers too and they got RPC service error so users couldn't connect. After a reboot, users can login domain again until next froze. 97% of our computers are running MS W2K professional and W2K server with 9/2005 security patches applied. System Admins said that our Trend Micro Antivirus is up-to-date and the Exchange 2000 and 2003 servers were filtering virus emails. We use HP SIM server. There are no particular errors in the event logs on PC's or servers. But during all this downtime, all our web applications and oracle database servers seemed to be OK. What could cause this problem? Can you please help?

Thank you in advance.

Best regards,
Jan Shu

[Jan Shu]

This is a duplicate thread.