I had this problem for a while, however it only became really annoying recently as I needed to forward a few ports.
My problem: I can't access the web interface of my router when typing 192.168.1.1 into a browser.
I tried rebooting the router, using a different browser, using a different computer, checking firewall and probably some other stuff that I don't remember since this is going on for a few years.
Yes, the router address is correct and yes, I'm in the same subnet.
No, there doesn't seem to be any other device with the same IP.
What's really puzzling me right now is that I remember being able to access it through telnet when the issues first started, however the connection is timing out now.
The only option that I have left seems to be factory resetting the router, however I do not want to risk losing TV in addition to the internet if I somehow won't be able to set it back up.