You can try buing another Ethernet card and disabling the one on the mainboard.  
Studio XPS 8100 running 64 bit Windows 7.  NIC is on the system board.  Windows detects the NIC but says a cable is unplugged.  There is a plugged in cable and it works fine on other computers if I just remove it from the Dell and plug into another computer.  Therefore the physical cable itself seems to be OK.  Have installed the latest drivers to no avail.  Have tried to run the Broadcom diagnostic software but it also says cable unplugged.  BIOS is updated to the latest version. Have tried turning off the Windows firewall but no effect on the problem.  Have tried changing from auto to full duplex but no effect either. I would yank out the NIC and replace it but that is not possible with it built into the system board. Any suggestions greatly appreciated.  Naturally the warranty ran out last month and no way I will spring for a new system board.  Just wanted to make sure I had an alternative way to connect to my network and internet other than wireless.
NIC Not Responding