Does not find any networks

We have a home network (recently switched to fiber optics, strong, fast). Our main TV is two floors down in the basement (router in my home office on the 2nd floor). No trouble connecting there - all WiFi devices connect from anywhere in the house to the home network. Except: right across the hall from my office is a bedroom with a Vizio TV, and, as with the basement TV, we use Roku. We could connect earlier (summer), but now can't connect at all; when we try to set up the connection, it can't find any networks at all (by contrast, my computer will show recognition of about twenty home networks in the neighborhood). How to get it to "see" the home network?