Network cable unplugged (but not)

[akaaren]

Hi, I've got a Dell laptop which I'm trying to connect to the internet. I've had it hooked up to dial-up and wireless before. I was on high-speed internet this spring, but the Comcast guy said that the ethernet port didn't work and so we hooked up the ethernet cable into the USB port. I've now moved, and the USB trick doesn't seem to work anymore. When I plug an ethernet cable into my ethernet port I get an error message that says that a network cable is unplugged. This message blinks on and off about once every 30 seconds. There will be the little icon with the computer with the yellow ball that indicates it's trying to connect and then I get the computer with the red X and the error message. Then the yellow ball computer comes back. This tells me that my computer is seeing the cable plugged in, but something else is going awry. When I used the USB port in the past, everything worked just fine. Now I've got an ethernet cable with a USB adapter. The same error message comes on and off!!! I know the rest of the system is good - cable, router, etc., - because other computers work with those components. Thanks for your help!