This can at times be cause by conflicting hardware, although rare. One thing to check: Make sure all computer have the same Network Protocols. If one is using an older Protocol, it will limit access from other computers, and remove all access to newer versions of the protocol on the network.
[[Network connections>View network connections>[Network used] right click>Properties>Install>Protocols]] it is best to install the newest of everything available. I wouldn't suggest installing anything but the protocols as the "Client and "service" can cause some other annoying problems (not sure how it ties in but one removes the normal log-in screen). Make sure they all have the same things installed.
If this isn't it, I am out of idea, but this is what I have learned in my network adventures. I had this same trouble not long ago, we have a network consisting of 6 computers, and 2 printers.