I have a NT 4.0 server (sp6a) with exchange 5.5 running (sp3). It is the PDC, file server and also runs WINS, rather than DHCP and DNS. From time to time, and there is no apparent pattern to this, it will begin to lock up. I first notice that while on the server explorer does not work. Then within a couple hours, if I goto server manager, it gives an error that the primary dc could not be located. Later, users are unable to logon to the domain, getting the "no domain server found" error. But they can get email from the server. Eventually the server worsens to such a state that nothing can be done on the server itself (hangs), and users cannot access any resources including email. Shutting down or restarting does not work. I have to hard boot in order to get the server working again, at which time it operates normally, after checking its drives. I really don't know what the cause could be. I suspect either network card, memory leaks, or something else. If anyone has any ideas as to what I can check for the cause, I would be greatly apperciative. You can reply here or send me an email. Thanks in advance. Joe.

Are you disinclined to applying Service Pack 4? http://www.slipstick.com/exs/exs55sp4.htm

Joe, Coming from a hardware background, this problem sounds to be related more with the machine than with Windows. I suspect a problem with how the memory is being paged. Is this a locally built unit, or from a big company i.e. Dell, Compaq, HP etc? I wonder if the RAM type is correct for the motherboard and BIOS in this system... Is there enougn RAM for all of the programs you are running? In the Task Manager you can see a chart of how much memory is being used at any given instance. How does this compare to the RAM installed, and how large of a Page file (swap file) is set in the system properties? One other thing I would do is to run a thourough version of chkdsk on each drive, as a precaution. A bad spot on a drive could cause these sypmtoms as well.