My Roku TV won't connect to WiFi.

There are some router setting issues that can prevent establishing Roku wifi connections. And to make matters worse, some of them can be caused by recently-reported router updates. These have primarily been reported with routers supplied by internet providers (Comcast/Xfinity, Cox, and AT&T so far), but it's possible they could also occur with other internet providers or user-owned routers that have received similar updates.

Your situation sounds like this one:

•  ROKU CANNOT FIND LOCAL WIFI NETWORK AT ALL
  If you have one of these situations, see "Reconfiguring Router", below.
   
  A) Some recent router updates have turned off dual band routers' use of the 2.4 GHz band. Some Roku models, notably Roku Express/Express+ (model numbers below 3940) and Premiere/Premiere+ (model numbers above 4620), are lower end units with single band Wi-Fi radios that only support the 2.4 GHz band. They, and many other devices of all sorts that are 2.4 GHz only, can't even see the 5 GHz band, let alone connect to it. If you have 2.4 GHz only Roku model and a dual band router with both 2.4 and 5 GHz bands, be sure the router's 2.4 GHz band is turned on.
   
  B) In the 2.4 GHz WiFi band, all Rokus support channels 1-11, as are used in North America. If your router supports 2.4 GHz channels outside this range make sure your router is set to use a channel in this range and that you aren't using an auto setting that could select channels outside this range.
   
  C) Rokus with dual-band wifi radios can connect to the 5 GHz wifi band in two ranges of channel numbers, 36-48, and 149-165.  Specifically they do NOT support the "DFS" channels 50-64 and 100-144.  If your router supports 5 GHz channels outside these two supported ranges make sure your router is set to use a channel within these ranges and that you aren't using an auto setting that could select channels not in these ranges.

Reconfiguring Router
Thanks to forum user AvsGunnarAvsGunnar  for providing the links below to instructions for reconfiguring router settings for the listed internet suppliers. If you can't do this yourself, you may need to contact your internet provider to make these changes for you:

• Xfinity / Comcast → ( https://www.xfinity.com/support/articles/change-wifi-mode-admin-tool-xfinity-xfi ) with a walkthrough ( https://community.roku.com/t5/Network-Wireless-Wired-Connections/Error-014-30-stuck-for-three-days/m-p/749057#M21380)
  
  
• Cox → (https://www.cox.com/residential/support/managing-your-in-home-network-with-my-wifi.html)
  
  
• AT&T → (https://www.att.com/support/article/u-verse-high-speed-internet/KM1046172). You can select your appropriate router from the drop down menu.

If your problem was not caused by any of the above, often a restart of the router (even if other devices are still connecting) followed by a restart of the Roku will allow the connection to be reestablished. Depending on your Roku model and Roku version number you'll find the "System restart" option under either "Settings > System > Power" or "Settings > System", or if more convenient you can just remove the Roku's power for a few seconds and let it restart.