The network in question has 3 domain controllers 2 are Windows 2003 Server and 1 is Windows 2000 Server. The W2k Server DC is in a remote location we will call T-Town, and has a Frame Realay connection to a location we will call W-Town. The other 2 W2k3 DC servers are in W-Town and on the same subnet. T-Town uses different subnet than W-Town but the DCs all work together to service requests for both locations and the Domain Name is the same at both locations. Basically the T-Town network is a remote extension of the W-Town network and has a DC in case the Frame Relay were to go down that way the networks could function independantly. The client machines all run Windows XP SP2 Pro.
In both T-Town and W-Town I can add machines to the domain and currently have no known issues whith the networks nor any of their resources. However it has happened twice now that two different users who from time to time take their Domain Joined Laptop home to do some work; have come back into the network to find that none of their network drives will map and no network resources are available to them. Also their computer no longer recognizes that the domain nor it's resources exists; However the machine can use the internet and I can use VNC to access the machine remotely, so the network card appears to be functioning properally.
I verified that the user was logged on to their machine with Domain Cerdentials. They were and were able to loginto the machine but likely using cached credentials, since I could not use a Domain account to loginto the machine that had not logged in there before.
I preformed a reboot of the machine and had the user logon (with Domain Credentials), log off and then back on again, attempting to ensure network card had properally initialized before login process began; This made no differance.
While logged in with User's Domain Credentials I was able to use the internet and ping network IP addresses sucessfully even those of the domain controllers.
While logged in as User I attempted to access several Network Shares. I was not able to and was not prompted to authenticate as one may expect you would be if the resource existed and there was problem with a security token or something of that nature, rather it could not find the resource as though it didn't exist.
I dropped the machine from the Domain and then attempted to re-add it to the domain. Upon rejoin attempt I would get an error stating that the domain controller did not exist.
I tried many other things that may not be relavent...
Then I booted the computer on the Windows install CD and did a repair on the OS, the first repair didn't work, the second level of the repair process did fix the issue and I was able to re-join the domain; however after a week of use the same thing happened again to the same computer. At this point I assumed that it could be a Virus because the machine had left the network both times. I ran several different AntiVirus and SpyWare remover tools and the computer came up clean every time. Finally I formatted and reloaded the system and it has been functioning fine since (about 2 months).
Now I have another computer that is doing the same thing and there seems to be no reason for it and it seems not to be fixable except for an OS Reload. This doesn't seem to be just a fluke and I am dumbfounded as to what can be causing it outside of a possible unidentified computer virus.
Assuming that a virus is not to blame, what is causing this, how can it be prevented and how do I fix it without rebuilding the OS?