Forum Discussion
To help rule out a hardware issue, verify that you have a seeing a MAC address under Settings/Network/About. (if you see all zeros, then normally a wifi card/module issue).
If MAC address is all good, try connecting to a mobile hotspot if available to you. If you can connect to mobile hotspot, then narrowing down to network issue.
If you are able to connect to mobile hotspot, then verify that you have not inadvertently "Paused" your internet connection for the Roku TV via any ISP (internet service provider) mobile app.
If you are certain you have not Paused the internet connection, and no other filters are applicable (ie. MAC address Filter), then make sure you are not using any DFS channels (52-140) on the 5ghz band as Roku cannot currently see or use DFS. I think this may be the least of the possibilities though since the Roku TV should be seeing/connecting to your 2.4ghz band if the 5ghz is unavailable. (unless your ISP has disabled your 2.4ghz w/o your knowledge, so may need to verify that both your 2.4ghz and 5ghz bands are working).
Feel free to post back with router model number and ISP if still having issues.