2000 Server Domain Controller Problems

I have a small 2000 sever netwwork with 2 domain controllers. I had one server go down and I took it off line for about a week. The other server took over the domain acitivities and everything was fine. Now when I bring the old server back on line some of the newer PC’s can’t connect. The two domains do now appear to be syncing up. The old was the master. When I try and connect to the damone controller I get the message The RPC server is not avaliable. Any help would be appreicaited.