Question Suddenly direct Ethernet connection to router not working, but via a 2nd router is fine.

Sep 27, 2019
I have a Windows 7 PC that had been happily connected (by Ethernet cable) to a fibre modem/router for about a year. This evening, I turned it on: no internet connection.

After some tinkering, a couple of things stand out to me as particularly strange:
  • The PC connects fine to the internet via Ethernet cable to a second router, which in turn is connected to the fibre modem/router. (This setup exists because the fibre modem/router doesn't have WiFi itself, the second router does).
  • My laptop connects to the internet fine over the direct Ethernet connection to the fibre modem/router (which the PC can't).
The first point demonstrates that the PC is still capable of connecting to the internet via Ethernet. The second point demonstrates that the direct Ethernet connection is capable of delivering internet. So, my best guess is that something has gone wrong in the configuration of the PC and/or the modem/router.

I've tried various things that seemed obvious:
  • Ran Windows network troubleshooter.
  • Rebooted the modem/router.
  • Rebooted the PC.
  • Checked basic connection properties (auto IP address, auto DNS server address).
I've also tried varyingly dubious ideas that I found online:
  • Reinstalled NIC drivers.
  • Flushed the DNS cache.
  • Winsock reset.
  • Ran virus scans (Malwarebytes and MS Security Essentials).
I had also hoped to log in to the modem/router to check if my PC had somehow been blacklisted or something, but it's some bizarre Swedish "Icotera" device and, as far as I can tell, it doesn't serve up any kind of web interface. (I tried browsing to the default gateway reported by ipconfig, but nothing happened). I'm in a rented apartment, so possibly I can't (or at least shouldn't) play around with the routers.

What could possibly have gone wrong? And how can I fix it?!

Many thanks for any help.
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