How do you connect a laptop computer to your hdtv through the cable box

If you are looking to to use your TV as a computer screen, it is really not a cable issue.  If your laptop has and HDMI output port just plug it in to an available HDMI input on your TV, navigate to that input and viola, there you have it.  If your computer does not have an HDMI output port, there are many USB to HDMI .  Hope this is what you were looking for,

you can't use your cable box to pass your laptop signal to the tv