Windows XP Home & "Network Cable unplugged"....HELP!?

Please please please could someone help?
I have recently converted from a dial up account to BT Broadband using the Voyager 210 router. I have had all sorts of problems but eventually mangaed to get connected through the USB socket on the router. I just could not get the ethernet to work whatsoever. The Ethernet card is said to be working fine in Device Manageron my machine but using the provided patch cable it just would not work. I have then tried to create a second connection on my daughters PC via the ethernet port on the router & the card (BRAND NEW and functioning perfectly in her Device manager) but I still keep getting "Network cable unplugged" messages on her PC. I tried reinstalling the router on her machine via the USB and it works perfectly. How do I connect hers to the router without getting the dreaded Network cable message? I even tried a USB to LAN (RJ45) adaptor to connect USB port on her m/c to the Ethernet port of the router but then I get the cable unplugged message again even though I know the USB port on hers to be fine! Any ideas to help solve this matter! Phew!
Dave