As was asked of the other users.. we would need a little more information.
A) how is your TV connected.. just from the wall to the TV, or is there a digital box?
B) if so, what digital box do you have?
C) what is the exact issue? Is there no picture at all on a channel? Is there a message? Is it jumpy? (picture then nothing at all), or is it all garbled?
I frequently have that problem with CP24 HD. It's been out all day today.
There was a time when a reboot would bring it back now even that doesn't work.
I should add that it's now 11:30 pm and we still have a black screen on CP24 HD.
The non high definition channel is working.