My Roku Philips TV will not find ANY wi-fi networks,

UPDATE: And something for Roku to look into.

I have an external hard drive I use for some old movies and photos plugged into the USB port of the TV. I unplugged that and decided to try the network scan again. Bingo. Found many of the networks/my network and connected fine.

Why would having a hard drive plugged in mess with the network scan/connection? Seems pretty sketchy.

Anyway. If it happens again I'll try unplugging anything from the USB port and see what happens.

[This was written at the same time you were writing your reply.  As long as it's here already I'll leave it in case it helps others]

never-again-

You might learn something useful for trouble shooting by checking your devices that DO connect to your WiFi to determine what channel number (and thus the WiFi band) they are connecting to.

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.

• ROKU LOCATES NETWORK AND REPORTS NETWORK QUALITY BUT CANNOT CONNECT
  
  never-again- This doesn't sound like it applies to you -- I'm just including it for the benefit of others who may be reading this thread.
  
  Some router updates have changed the router's connection settings on the 2.4 GHz WiFi band from b/g/n to just g/n, causing Rokus connecting to the 2.4 GHz WiFi band to lose their ability to connect to the network.
  
  Note that, of recent Roku models, non-4K Roku Express/Express+ (model numbers below 3940) and Premiere/Premiere+ (model numbers above 4630) can ONLY receive the 2.4 GHz band and are therefore affected by this.
  
  The solution is to set the router's configuration back to using b/g/n.  See "Reconfiguring Router", below.
   
  • ROKU CANNOT FIND LOCAL WIFI NETWORK AT ALL
    If you have one of the situation discussed below, 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 4630), 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 12-14 that are used in some other regions, make sure your router is set to use a channel in the 1-11 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.  The channels assigned to the 5 GHz band in channel ranges 50-64 and 100-144 are shared with other uses such as military, radar, and weather. These channels are termed DFS (dynamic frequency selection) channels and routers are supposed to automatically switch to a different channel if they detect one of these channels is in use in your area. Most Roku models and many other home use devices don't support these DFS channels.
    
    Roku added support for DFS channels to those models newer equipped to receive them in Roku version 12.0.  Roku models capable of running Roku 12.0 that but are NOT equipped to receive DFS channels are:
    3600X, 3800X, 3811X, 4200X, 4201X, 4205X, 4210X, 4210X2, 4230X, 4230X2, 4620X, 4630X, 4640X, 4660X, 4660X2, 4670R, 6301X, 6302X, 6303X, 6102X, 6103X, 6104X,, 6106X, 6107X, 6108X, 6109X, 6110X, 6112X, 6113X, 6114X, 6402X, 6403X, 6404X, 6405X, 6406X, 6407X, 6408X, 6409X
    (Source: https://support.roku.com/article/115015760328)
    
    Many home use modems do not include the DFS channels but some do, so if your Roku model does not support DFS:
    •  Be sure your modem is set to NOT use DFS channels.
    •  If your router supports DFS channels and you can't turn them off, make sure you aren't using an auto setting that could select DFS channels.

Reconfiguring Router
Thanks to forum user AvsGunnar  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 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.