Domain Login

I have 2 buildings, Seperated by 3 miles, connected via dsl routers. Building 1 end is the server, and building 2 is other workstations that need to logon to building 1 server. I can do a \\Server\Share and see building 1 from building 2 but cannotlogon to server. Keeps saying no domain server availeble. I can ping both sides, and I have tcp/ip. I will update this a bit later, but any help would be great.