Lost internet

Two days ago I was exploring router settings, trying to better my slow 8 Mbps speed. I was in the QoS setup section, disabled WMM and attempted to enable QoS downstream. At some point, my internet connection was lost (not sure of the exact sequence of events immediately before this occured). The R6400 UI shows Interent Not Connected on the basic page and  the power and internet leds are amber. No IP address is being picked up by the router now. I've power cycled the network a number of times, restored a backup cfg file to the router and done a hardware reset on the router, all to no avail. Hooking my wife's laptop to the modem (a CM400) with an ethernet cable, shows the modem is receiving the signal from Comcast (internet works). Router's wifi is working but no internet is available to any device via wifi.

I've read through several threads but no luck in applying those ideas to my situation. What am I overlooking?

Thanks.