You didn't say which Roku device you have. The model number is always helpful. Settings > System > About
If it's an older Roku Express, or some other similar older models, it may operate only on 2.4 GHz band. Many ISPs are either disabling or changing from traditional settings on 2.4 GHz band. Roku requires b/g/n settings, and some ISPs are using g/n only, or not 2.4 GHz at all.
See if this might be what's going on.
Roku Community Streaming Expert
Note: I am not a Roku employee.
If this post solves your problem please help others find this answer and click "Accept as Solution."