Any time the NIC autonegotiates to only 100, it usually means a mismatch in settings. Especially if forcing to 1GB makes it go offline.
What are the settings on the router port, do you know?
Thank you for your help.
I think all the settings in the router are default. Is there a way to check the router's port?
However, there's another PC at my home with Atheros LAN and G31 chipset. That one can reach 1Gb/s without me doing anything to it.
To check the router port configuration, you have to be able to log in to the router's IP address, and know the username and password.
I do recall, from long long ago, that there would occasionally be other adapters that would link with some network cards, but not all. However, updating all the firmware, on all the hardware (network card *and* router) usually fixed it.
You have tried the same cable that works with the Atheros, with the Intel, right?
It's also possible the physical Intel port might be on its way out.
Thank you very much. It was really the problem of the cable.
I used another cable and it works fine now.