Hello Hudalus,
I would first connect to the Internet Box Fiber’s web interface (using your Mac). You find all login information on the sticker under the Box.
Then connect the PC via Ethernet cable and check if the chosen port’s lights turn and stay off from time to time for several seconds, just like the link gets interrupted.
If this is the case, you have something in Windows disturbing your network adapters (networking and related service(s) crashing and restarting, network adapters’ driver crashing, …).
On the web interface, check if the PC is visible and has a valid IP address. If not, you need to check your Windows PC’s TCP/IP settings.
Please note that Windows 10 has two “layers” of networking configuration that may conflict each other.
On Windows 10’s Settings -> Network & Internet you can check both Wi-Fi and Ethernet connections where you can see and modify your TCP/IP properties (that should be set to “Automatic DHCP” to work correctly with the Internet Box Fiber).
Then, on Windows’ “classic” Control Panel you can access “Network Connections and Sharing” pane and under “Network Adapter Settings” you will find both your Wi-Fi and Ethernet adapters.
Now, if you right click on adapter’s icon and choose “Properties” -> "Internet Protocol 4 (TCP/IPv4) you will find the second (deeper) “layer”.
Please check that “Automatically obtain IP address” and “Automatically obtain DNS server” are selected and then click on OK.
Hope that helps.
Kind Regards,
cande