gigabyte Z77X-UD3H has no ethernet connection,says it needs a driver ,but can't download if one is found.?

I'd start with the installing the drivers from the disc that came with the mobo. If that doesn't help, check to see that LAN/WAN isn't disabled in the BIOS. You could also use a computer that has a network connection to download the latest drivers, or check the mobo manufacturer's website to see if there is a BIOS update that addresses this concern. As a last resort, you can contact the mobo tech support for possible RMA.