I have had this problem on 2 separate Fujitsu LIFEBOOK E734 Notebooks. Fujitsu support for Windows 10 is poor, and there are no drivers published.
The issue is:
– After upgrade to Windows 10 from Windows 7 (either a clean Windows 7 install or the Fujitsu pre-installed image), the network card looks fine but does not work, DHCP cannot get an address and a manual IP cannot communicate. Uninstalling the adapter does not work. Consequently, it is not possible to activate the system, or do anything else for that matter, unless Wi-Fi is working.
The fix, is unfortunately to do a clean install. After clean install it works fine, but this can only be done once Windows 10 is activated (in order to retain Windows 10 activation status), which is tricky if there is not network. See http://www.msdonkey.com/windows10/performing-a-clean-install-of-windows-10/ for more info on doing an upgrade and then clean install.
Using Wi-Fi did work for me, so the issue seems to do with the Ethernet card and not the whole network stack.
So in summary, there is an issue with upgrading the Fujitsu E734 with Intel I217V Ethernet card, and others may also have this issue with this card. I recommend doing a clean install after the initial upgrade, but make sure that Windows 10 is activated first – try using Wi-Fi to do that