Your post implies you previously had a non-wireless connection, which would mean you have a model with an Ethernet jack. That, in turn, implies you have a model that supports both wifi bands, 2.4 GHz and 5 GHz, since the less expensive models with only 2.4 GHz don't have Ethernet jacks.
I can't help you specifically with a Comcast modem/router, but I can tell you Rokus will only connect to channels 1-11 in the 2.4 GHz band and channels 36-48 & 149-165 in the 5 GHz band. If your router is set to use channels outside these ranges, the Roku won't connect. The router may also be set to auto-select the channels it uses, and could be setting you, or switching you to, one the Roku can't use.
Roku Community Streaming Expert
I am not a Roku employee, only a user like you.
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