Sycnchronizing with the PDC

We have a BDC that will not sync. We can ping the IP of the BDC, but we can not see the BDC in the svrmgr. The users log on through this BDC. They can see all of our shared drives and their Outlook is working. If a user password expires we can notchange their password. This is a remote BDC, but still connected to our network.
When we bring it to our comm-room it works, but as soon as we take it back to its location it want snyc and we can not see svrmgr.