All network conections fail to connect

When I switched on my computer, I was presented with a message saying that the Ethernet was not connected, I tried changing the cable, and also trying the second ethernet port on my computer. After this I still was unable to connect to any network, I tried to teather my mobile phone (samsung galaxy s2 w/ cyanogen mod) via USB this installed correctly and claimed to be working as an interface in the network connections window of cpntrol panel but yet there was still netwrok. I checked to see if there had been any updates installed but none had been installed for over a week.
Anyone have any ideas or should I just reinstall windows?
Thanks.

Antivirus : Zonealarm extreme security
ISP : Virgin (internet still available to other computer on the network)
Router : Netgear WNDR3300

First thing i would try even though you say the 2nd computer connects fine; I would try power cycling both the modem and router. Unplug both of them, wait about a minute, then plug the modem back in first and let it boot; then plug the router back in and let it boot. Second, check for any firmware updates for the router as that also may correct the problem. third; on the computer that has the issue; go into the device manager and double check to make sure there are no check marks or exclamation points by any of the ethernet cards/connections. If there are; i would uninstall them, reboot, and let windows try and reinstall them correctly as its possible something happened during the operation of the card like something somehow got corrupted. Try these things and see if they help any.

well; from what i researched on google just now; it could be a corrupted file from a malware scan or something along those lines. Try this: click start, programs, accessories, then right click on command prompt and select run as administrator and type sfc /scannow