I installed Windows 8 on my desktop which is running on Windows 7 too. It's dual boot. The problem was in my Ethernet cable (Realtek), when I run windows7 everything's cool but when I go to windows8 it seems that it won't detect my cable. There's no "light" at the back and it says "ethernet cable unplugged". I already tried re-installing the network driver from the CD that comes with the motherboard (MSI FM2-A75MA-P33). I also tried changing the Speed Duplex thing - didn't worked. Also disabled 'Fast Start' - didn't work too. I'm sooo stressed with this Please help.
Make a clean installation of the drivers!
As Far As I know,Windows 8 don't need Ethernet drivers to be installed ( as per my experience). Download the compatible drivers only. Perform clean installation.
Here, try this link http://www.msi.com/service/download/driver-19240.html