I do not know about your situation, as you haven't really given enough information. That being the case, it could be a number of things. For one thing, are you having the slow NPL issue? If so, the other dvr's will not show up in the list for about 30-45 seconds.
Anyway, I would say that you will probably need to start out by taking a serial cable and connecting to your receivers, one by one and go back thru the process of assigning the IP address for the receiver. I recently had my computers, router, and stuff disconnected recently. When I hooked everything back up, I had the slow NPL issue, and tivo server could not see my receivers at all. I connected the cable to each one at a time, and went back thru the part of assigning the ip address. Then rebooted the receivers, and the fixed both problems.
But, like I said, it all depends on your situation. This is why we really need more info.