|How is your network setup? What sort of modem/router do you have? When you say directly connected to your modem is that via a switch on the modem or other means? Are your computers statically assigned or are addresses provided by DHCP? Are you running any firewall indipendantly (smoothwall, IPCOP etc) or are there rules on your modem/router that could be causing problems?|
The fact that when the computer 'is plugged directly into the modem' and works throws me off a little with troubleshooting. I was thinking firstly to check the line and connections on your network, then DNS. Try a ping -t to your dns server from the command line to see if you have any packet loss. Other than that if there is no firewalls, line faults, DNS server issues then its going to be hard to fault find.