Issues with Network

[FelicityCM]

Hi, I am running leopard 10.5.2 and for a while my network was working fine, the mac is connected to 3 pcs via a network cable set up with ethernet and manual IP addresses for so long this was fine it would show the networked machine in the other devices panel but recently it is no longer showing them. Sometimes they show up and sometimes they don't I know for a fact that one of the pc's is on and therefore should be showing in my devices panel but it isn't. Also whenever one of the machines turns off it lets me know on my mac and says disconnect so I usually click that and usually when it comes back on it shows that its there but lately it is no longer doing that. Does anyone know how to fix this? Do I need to change my network settings? (I would prefer not to use airport)