network not accessible

Have a peer to peer network with 3 windows 2000 machines and 1 windows 98 se machine. Windows 2000 machines don’t always see the network. Out of the 3 windows 2000 machines, 1 seems to be unable to browse the network most often. There dosen’t seem to be a specific reason for the 1 machine not to be able to browse ,ie. most of the time the 1 pc that can’t browse is usually the first one booted up in the morning. But it’s not always the first to boot up so I cant tie boot up order to the specific problem. All 3 windows 2000 machines are running SP3. I’m kind of baffled to the cause of this problem. All pcs are on the same workgroup and on the same subnet. Thanks for any input.