With advancing age there seem to come more "Duh!" moments - or in the current Internet parlance, "Derp!" moments. The other evening our daughter complained she could not get an Internet connection. All of the attached devices in our house are wireless, except the "main" computer - which was working fine, as were the other computers. It was apparently not a problem with our actual Internet connection.
After some standard fiddling around, I remembered I also had some wireless problems with a different computer a couple days before (which worked fine the next day). Neither that one nor my daughter's PC were responding to the "normal" things; repairing the connection, rebooting, etc. After some head scratching and grumbling, it dawned on me that I had restricted the number of wireless connections on our LAN from the default 255 in the router settings; after a quick finger count of computers, game systems, an iPhone and a Kindle, I realized we simply had one too many devices connected.