You need to replace your hub with a switch, and the other 3 computers should also be on a switch instead of a router, technically speaking. There is only a need for a router at the ingress point to your LAN from the internet, to be used as a gateway. A switch is better suited to handle full duplex traffic from multiple hosts than is a router. With that many computers on a home network, I would recommend getting two gigabit switches and CAT6 cable if you can afford it.
Have you checked the settings on that other computer?
If the other devices connected to that hub are fine, then it's probably the computer that's at fault. Check to see if it's getting an IP address, and if the web-browser knows what connection to use to access the Internet.
Get the hostnames of other machines on your network, and try pinging them from the red machine. That should help you begin to troubleshoot any serious problems.