Do you mean channels from a cable box to the DVD unit?
Then the DVD unit isn't receiving any of those cable channels.
Then when you connect to cable box directly to the TV & you are able to receive the channels.
Going with thor21344 can you play a DVD disc to the TV ?
If the TV is able to receive directly from the cable box & you are using the same HDMI port as the DVD unit usually uses for the connection. There shouldn't be a problem with the TV.
My suspicion is the DVD player input has changed for some reason .
Meaning it expects it's signal from a RF cable instead of HDMI fo example.
Of course if you can't play a DVD disc & receive that on the TV then the DVD player output is the problem.