Which activity LED - on the modem, router or network card?
What OS is the PC running? The USB drivers shouldn't affect the ethernet connection, but if you're not going back to USB you could follow
http://homepage.ntlworld.com/robin.d...tml#usbdrivers to uninstall the USB drivers.
When all the devices plugged in and turned on above, can you browse to
http://192.168.2.1
This is the user interface of the Belkin.
If you can get there, can you also get to
http://192.168.100.1/config.html - which is the Surfboard UI.
If not, can you post the results of 'ipconfig /all' and 'ping 192.168.2.1' from the PC.
HTH