|You may need a different set or drivers for your your Windows 8 installation, certainly at least the Windows 8 installation does not 'see' the drivers installed on the Windows 7 installation. Some Windows 7 drivers may work with Windows 8, but do not count on it always being the case. If Dell does not specifically list Windows 8 driver for the LAN but all of your other drivers work (chipset, video, etc.), you may very well end up purchasing a new LAN card that does have Windows 8 driver (check their website first for the download before purchasing) available and use that card for both W7 & W8.|
I am assuming that you looked in Device Manager for details, uninstall the device, and allow Windows to reinstall it after installing the new driver.
You have to be a little bit crazy to keep you from going insane.