are you sure you have link between the devices. It sound like you are using dhcp to assing an ip address to the nic that is attached to the network. as a recomendation this should be a static ip assignment. this is going to be your gateway for your network and a dhcp assingment can change. Not that it will but it could. Not sure if this is your situation but it is a recomendation. have you check the cables and know they are good? there just isn't much information here to go on so just shooting in the dark...