I'm using a Zyxel Prestige 660RU-T1 modem, supplied by the service provider, and I am having a frustrating problem for the last couple of months without any real reason why.

I have the modem beside the phone socket, and a 7m ethernet cable running to the PC. Through this, there is no connection. Packets are sent, but none received. However, the moment I plug a laptop into the USB socket on the modem (while the ethernet is still connected), both the PC and laptop have perfect connection.

This leads me to conclude that my ethernet cable and network card are in working order. Also, I have replaced the modem with an identical model and this has worked in the exact same way. We had this problem with another modem, a few months ago, and the SP replaced the modem. So we're talking about 3 Zyxel modems having the exact same issue.

Is there any logical reason why this is happening? Even any theories?

Thanks a lot,
Fionn