R6700 WiFi won’t detect

> R6700 [...]

   R6700[v1], R6700v2, or R6700v3?  Look for "Model" on the product
label.  Firmware version?  Connected to what?

> I have WiFi; [...]

   I don't know what that means.  You have some kind of computer/device
which has a wireless interface, or what?

> [...] WiFi still not picking it up. [...]

   I don't know what that means.  As usual, showing actual actions
(commands) with their actual results (error messages, LED indicators,
...) can be more helpful than vague descriptions or interpretations.

   Do other devices work better?  Does your problem device detect other
wireless routers?

> [...] How can you tell when there is a problem with the router? [...]

   You might start with an oft-neglected resource:

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

   Visit http://netgear.com/support , put in your (actual) model number,
and look for Documentation.  Get the User Manual (at least).  Read.
Look for the LED descriptions and "Troubleshoot".  Pay particular
attention to something like the "WiFi On/Off button with LED" or "WiFi
LED".  Did you press it?  Further reading might not hurt, either.

> [...] Typical shelf life? [...]

   "shelf life" is when you're _not_ using it.  But there is no
well-defined lifetime for such devices.