X1 or legacy cable box? What does remote say on back for code?
First thing: power cycle cable box. (Unplug power cord and then plug back in.) Once box working again try the remote. Working?
For an X1 box try this: hold setup till light on remote turns green, then hit Xfinity button. Type 3 digit code. Hit "skip" for the next two options. Does it work now? If not you probably need a tech.
For a legacy box, what kind of remote is it? Silver or black? If silver, make sure "cable" button is pushed before trying a channel change. Work? If yes, it could be that the "channel lock" feature is disabled (you'd have to google how to fix channel lock on a silver comcast remote). If no, does it have an XR8 plugged into the back of the cable box? If so, it could be malfunctioning. XR8 is a device to allow radio frequency pairing between cable box and black remote instead of infrared. If there you could try to re-pair it-->press button on XR8 and see that red light came on. Now hold setup button on remote until light turns green then hit Xfinity. You'll know it worked if you get a pattern of three green lights in a row at the end. If it goes red green red it did not work (and may not work). If it does not work remove the XR8 and that should resolve it.
Hopefully that helps.......
Need help. Remote want change channel
unplug the set top box and after 15 seconds plug it back in.
Jameshilton, were you able to get the remote to respond with RustyBen's advice?