It's hard to understand what you are doing based on your description.
I assume you have Humviewer on your PC and you are trying to use your
big screen TV to view it with.
You probably need some type of converter between your pc graphics output
to your big screen TV input. You probably have Video In(yellow) on the big screen.
I'm not sure, but you may even have RGB inputs on your TV which may be
better than Video. Depending on how new your TV is, you could have something
even better.
I would take your owners manual for both your computer, big screen TV, and maybe
even the computer graphics card (if available) to radio shack.
Tell them you want the very best resolution you can get from the pc to the
big screen, and let them tell you what you need.
They may recommend you changing your computer graphics card.
Good Luck.