Server dropping off of network

I run a somewhat small network with 5 servers and 45 workstations. The problem I’ve been having recently is one server (fileserver)which is also a BDC, is dropping off the network for apparently no reason. There is nothing in the event viewer or anywhere else that I can tell. I receive no errors other than “the specified device/path/drive cannot be found” when attempting to access a drive from within the network. I reboot and it usually comes back up and is fine for anywhere from a few minutes to a few days. Weird, I’m baffled. Any suggestions?