Double check to make sure issue is not with the physical cable. Try connecting a laptop or another machine to it. Do you get internet?
If so issue might be with the type of driver used or with the NIC port. Try another driver if that doesn't work maybe NIC got fried some how? Try a 3rd party NIC (cards are cheap nowadays).
Remove the duel boot. Take out all hard drives except for the one with Windows 10. Do you still have NIC and other issues? Is this a new SSD you are installing on? Maybe do a diag test on it.
As for the symbols. Are you sure you flashed the BIOS with the correct firmware? Honestly the only time I've seen that is when there was an incorrect firmware flashed onto it, or the mobo was dying...
The symbols along with...