Facing TV Problems? Ask a TV Technician.
Hi and welcome to the site, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.
Initially, bear with us; re-confirm and post back with the complete model number of the "...Comcast cable box..." Additionally, please describe how the cable box is connected to the TV using what kind of cable(s).
Appreciate the additional information.
That a "...Motorola cable box with coaxial cable... is connected to the Vizio E40-D0, then the Vizio would have to be set to TV mode / Ch 3 (or 4).
Are you able to go to Ch 3?
...or at least go to Settings Menu?
If already programmed, then pressing the + CH - buttons on the basic remote should cycle through the available channels including 3 and 4.
Then the Vizio would have to be paired with a smartphone or table that would serve as a full remote.
Alternatively but depending on the Motorola's model/features, the cable box may be connected using yellow + red & white RCA-to-RCA cables instead of coaxial cable.
What is the Motorola's model number please?
How about a picture of the Motorola's rear please? Click HERE.
Alternatively, please upload to imgur or Dropbox and post back here with the link(s)
Post back an update if and when conveniently able.
...and Happy New Year!