I have two Roku boxes and until this past weekend they were both working fine. Suddenly, on August 14, both devices simply stopped working, saying there was no Wi-Fi signal available. Other devices, such as laptops and phones, still recognize the Wi-Fi. I can connect my Roku to my iPhone using The iPhone as a hotspot but it does not see the router. There has been no change in the router settings. Seems like a lot of people are having this problem, and every once in a while, somebody from Roku logs in and asks a lot of questions about your device model, etc., which is a good way of not responding to the issue. This is clearly a widespread problem.
Your Model number and typs do matter to those trying to help.
Its not hard to mention I have an Ultra.
Does your Router broadcast a 2.4G signal?
No guarantees, but this has always worked for me when I've needed to re-establish the WiFi connection on a Roku device:
Reboot your router (Yes, do this even if your other devices have no problem finding and connecting to your network.)
When your router comes back up, restart your Roku via:
Separate Roku device: Settings > System > System restart
Roku TV: Settings > System > Power > System restart
Reconnect to your network via Settings > Network > Set up connection
If this still doesn't work, try pulling the power plug on your Roku for a minute or so then plugging it back in. When it's finished restarting, try to reconnect the network again.