First off, you mention an ethernet hub...do you mean the router or do you have a hub connected to your router, and the XBox connected to the hub?
1. Make sure you are not using a crossover cable.
2. Reboot router after connecting XBox.
3. Try a different cable.
4. DHCP on router enabled?
5. All items on the XBox's network menu set to "Automatic"?
6. Your router may not be compatible with the XBox. Try a different router.
This is the router i currently have for my internet.
I am trying to get onto Xbox live on my 360, by plugging a CAT5 cable into the ethernet hub, which i had always done to get onto Xbox live on my old Xbox. Whenever i test connection, it says hardware cannot be found, and i notice there are small lights on all the ethernet hubs that are not coming on. Unplugging the router and plugging it back in causes them to turn green, which im assuming means its working, but they turn off after about a minute. Anybody have any ideas?