Wired connections to NightHawk R7900P Won't connect to internet

What modem/gateway do you have it connected to? 

have you tried simply powering off the R7900P and rebooting it? 

> [...] I tried the QoS setting on my router and it changed my wired NAS
> and other devices addresses to something different (172.....) instead of
> the router defined IP addresses of (192.....). [...]

   It seems unlikely that a QoS setting could affect any IP address.  I
suspect that you did more than make a QoS change.  I would not expect an
address like "172....." to come from your router.  And there's no need
to hide any of a private address:

      https://en.wikipedia.org/wiki/Private_network

> [...] I am thinking of doing a router factory default reset. Would
> this be a good idea?

   Should be harmless, other than forcing you to reconfigure the thing,
but I wouldn't expect it to solve this problem.  I'd review what's
connected to what.  If necessary, start again, with the router and a
computer, and then build up your more complex network, stepwise, until
the problem reappears.