How about switching off your modem? I think I experienced the same thing - my iPhone and my Mac both began reporting failure on attempting to connect to my WiFi router (Airport Extreme, 2 or 3 years old). Lucky for me I have two Airport Expresses to extend my network, so I still had WiFi. Oddly, I found that one of them, which connects to my router only wirelessly, was still working; the other one was connected via Ethernet and was also fine. After seeing your post here, I aimed Wireless Diagnostics at the main router, but it wasn't able to "diagnose" because it couldn't connect. Trying Internet settings in various devices I got messages to the effect of "this device has no IP address." So I think I may have been having the same problem as you. I recently updated to OS X 10.9.2, but don't know whether that caused the problem. After re-booting all devices & computers, no joy. So I shut things down and did one step you don't list above: I not only unplugged power from the router but also switched off the modem. Left everything off while I started cooking dinner. After about ten minutes I first switched the modem back on, then waited a few minutes and plugged the power cord back into the router. When I restarted the computers and i-devices, everything was fine. Did you try that step of switching off the modem?