We have multiple macs and PCs on a network with a Windows 2000 server. We have been running macs on this network since 2008, replacing PCs with macs as we go. Up until a few days ago, everything worked nicely, then the macs could no longer connect to the server. We noticed the problem in the middle of the day. It worked in the morning, and not since. The macs are mostly minis, 2 iMacs, and an MBP. All but one of the minis are running Yosemite. The problem is identical for all the macs. The 3 PCs are not affected. No changes were made to the server, it stays powered on, but logged off. We can ping the server through Network Utility, and we can access the server through Virtual Machines and Microsoft Remote Desktop on the host macs, but not from OSx. We are able to see the server in the shared items in finder, but when we click to connect, it says Connection Failed. We have tried connecting as different users with no luck. We also have some alias shortcuts to folders on the server, when we click on those, it runs through the "Resolving alias to..." then asks for user name and password. None of our user names are working. I've spent over 9 hours on the phone with Apple, Microsoft, and even VMWare to find a solution, but everyone is stumped and has pointed to the other guys. Any help would be appreciated.